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Materials Science
in Construction:
An Introduction
Materials Science in Construction:An Introduction explains the science behind the properties and behaviour of
construction’s most fundamental materials (metals, cement and concrete, polymers, timber, bricks and
blocks, glass and plaster). In particular, the critical factors affecting in situ materials are examined, such as
deterioration and the behaviour and durability of materials under performance. An accessible, easy-to-
follow approach makes this book ideal for all diploma and undergraduate students on construction-related
courses taking a module in construction materials.
Ash Ahmed is a senior lecturer in construction materials science and module leader of several
undergraduate and postgraduate materials science modules at the School of the Built Environment and
Engineering at Leeds Beckett University. His research specialises in the evaluation of the mechanical and
physical properties of commercial materials as well as novel sustainable materials in civil engineering.
John Sturges is a visiting professor at the School of the Built Environment and Engineering at Leeds
Beckett University. His research interests include the environmental impact of materials, the energy
efﬁciency of buildings and the whole area of sustainability and its impact on UK industry.

This page intentionally left blank

Materials Science
in Construction:
An Introduction
Ash Ahmed and John Sturges

First published 2015
by Routledge
2 Park Square, Milton Park,Abingdon, Oxon OX14 4RN
and by Routledge
711 Third Avenue, NewYork, NY 10017
Routledge is an imprint of theTaylor & Francis Group, an informa business
© 2015 Ash Ahmed and John Sturges; individual chapters, the contributors
The right of Ash Ahmed and John Sturges to be identiﬁed as authors of this
work has been asserted by them in accordance with sections 77 and 78 of the
Copyright, Designs and Patents Act 1988.
All rights reserved. No part of this book may be reprinted or reproduced or
utilised in any form or by any electronic, mechanical, or other means, now
known or hereafter invented, including photocopying and recording, or in any
information storage or retrieval system, without permission in writing from the
publishers.
Trademark notice: Product or corporate names may be trademarks or registered
trademarks, and are used only for identiﬁcation and explanation without intent
to infringe.
Disclaimer: Every effort has been made to contact and acknowledge copyright
holders.The authors and publishers would be grateful to hear from any
copyright holder who is not acknowledged here and will undertake to rectify
any errors or omissions in future printings or editions of the book.
British Library Cataloguing-in-Publication Data
A catalogue record for this book is available from the British Library
Library of Congress Cataloging-in-Publication Data
Ahmed,Ash.
Materials science in construction / Ash Ahmed and John Sturges.
pages cm
Includes bibliographical references and index.
1. Building materials. I. Sturges, John (Construction engineer)
II.Title.
TA403.A34 2015
691—dc23 2014007765
ISBN: 978-1-85617-688-0 (pbk)
ISBN: 978-0-08-095850-7 (ebk)
Typeset in Bembo
by Keystroke, Station Road, Codsall,Wolverhampton

v
Contents
1 Introduction 1
PART I
Basic principles: material structures and properties 15
2 Bonding and structures 17
3 Dislocations, imperfections, plastic ﬂow and strengthening
mechanisms in metals 29
4 Mechanical properties of materials 51
5 Microstructure and phase transformations in alloys 67
6 Thermal properties of materials 78
7 Structures: shear force and bending moment diagrams 95
Philip Garrison
PART II
Individual types and classes of materials 119
METALS
8 Ferrous metals 121
9 Non-ferrous metals 134

vi
Contents
INORGANICS
10 Glass 138
11 Clay brickwork 154
Anton Fried
12 Concrete 172
Anton Fried
13 Autoclaved aerated concrete 193
ORGANICS
14 Polymers: properties, structure and characteristics 207
15 Polymers utilised in construction 228
16 Timber 241
17 Soil as a material 261
Martin Pritchard
18 Composite materials 279
PART III
In-service aspects of materials: durability and failure 297
19 Failure 1: effects of stress and applied loading 299
20 Failure 2: environmental degradation of materials 319
21 Failure 3: effects of ﬁre on building materials 341
PART IV
Conclusion: sustainability of materials 357
22 Environmental impact of materials 359
Index 382
vi

1
1
Introduction
This chapter provides an overview of mankind’s use of materials,comparing the use of materials in various
industrial sectors,and making clear the point that construction is the world’s largest consumer of materials.
It goes on to examine the importance of material properties in their selection for use, and outlines the
various types and classes of materials and their importance in construction. A discussion of the service
behaviour of materials and the problems of degradation and failure follows. Finally, in view of the current
importance of sustainability, their environmental impact is stressed, and an outline of the book’s contents
brings the chapter to a close.
Contents
1.1 The industrial use of materials 1
1.2 Importance of construction materials 2
1.2.1 Brief history of building materials 5
1.2.2 The materials of construction 7
1.3 Properties of materials 7
1.4 Behaviour of materials in service 7
1.4.1 The use of materials and their impact on the environment 11
1.5 The contents of this textbook 12
1.6 Critical thinking 12
1.7 Concept review questions 13
1.8 References and further reading 13
1.1 The industrial use of materials
The science and use of materials is central to all branches of industry, and as such is a subject of enormous
importance.The range of materials we have at our disposal is enormous,and is being added to as the results
of research and development are put to use week by week and month by month.The industries using
materials include construction, aerospace, automobile, shipbuilding, white goods, electronics, railways, etc.
Each industry has its own particular concerns about materials; in the aircraft business, the over-riding
concern is with lightness and weight-saving,with cost being secondary to this.This is well illustrated at the

2
Introduction
present time with the advent of the Boeing 787 Dreamliner,which is pioneering the use of fibre-reinforced
composite materials instead of the usual aluminium alloys for the construction of the airframe.Although
aluminium is already a light metal, its use is being abandoned in favour of fibre-reinforced polymeric
materials which are lighter still.
In the automobile industry, the luxury car sector currently is turning to the use of aluminium alloys for
body structures in place of the traditional steel, and again the driver for this is weight-saving, with the
consequent saving in running (fuel) costs. This may well be the precursor for the wider, progressive
replacement of steel with light metals or reinforced polymers. In the construction industry, the leitmotif is
most often low cost, i.e. weight-saving is not usually an issue, whereas keeping costs down to a minimum
is very important.Having said this,in the construction of very tall buildings,engineers do take steps to save
weight, usually in the construction of the upper floors of skyscrapers, in an effort to reduce the enormous
loads that need to be borne by their foundations. Steel and concrete are such popular materials in
construction; steel possesses high stiffness, high tensile and compressive strength and good ductility, with
prices starting at around £500 per tonne, and concrete represents the cheapest way to buy one unit of
compressive strength. Both are excellent value for money and this is most important in construction.
Each industry has its own preoccupations with the types of materials used. In most cases the products
made will be created in a well-regulated, factory environment. In construction, on the other hand, the
product is created on site in a less well-regulated environment, and this factor must be borne in mind. In
most industries materials can be tested before they are used, to ascertain their quality and fitness for
purpose. In construction, however, concrete falls outside this rule as it is made and used on site in one
operation. If serious mistakes are made, the defective piece of concrete may have to be broken out and
replaced.Concrete is the most widely used material of all,with over 12 billion tonnes being used worldwide
each year,and yet it differs from all other important materials in not being able to be tested before it is used.
Construction also uses a lot of timber, a traditional construction material which has been used for
centuries.We often lose sight of the fact that timber is a‘smart’material when it is growing as part of a tree.
In a growing tree, timber can sense where compressive stresses are increasing due to weight increase
brought about by the growth of new timber, and is able to respond by increasing the size of branches that
are bearing the increased weight. So far engineers have not been able to produce such a remarkable
material.
Finally, we must remember that whatever the industry using and specifying materials, what they are
really doing is specifying desirable properties.We shall return to this fact later. It has been estimated that we
currently have between 40,000 and 80,000 different materials (Ashby, 1992) at our disposal, if we count
separately all the different alloy steels, all the different polymers, species of timber, types of glass, types of
composites,etc.Making the correct selection can be a complex matter.Furthermore,for certain applications
we cannot always meet our requirements from single materials among the 40,000–80,000 available.
Sometimes none of these have the particular combination of properties we need; in such cases we may
have to make recourse to composite materials; we shall look in more detail at these later in the book.
1.2 Importance of construction materials
In the UK, the construction industry is one of the largest, employing 1.0–1.5 million people (Harvey &
Ashworth, 1997), and it rivals the NHS in size. It is responsible for at least 8 per cent of the UK’s gross
domestic product, currently being worth in excess of £60 billion per year. Roughly half of the industry’s
work involves new build, while the other half is maintenance, repairs and refurbishment. In addition, there
is the UK building materials industry: brick-making, cement production, steel-making, as well as the
industries that produce glass, plastics, gypsum plaster products, timber products, paints, fasteners, etc.
The construction industry in the UK consists of over 170,000 individual companies, the over-
whelming preponderance of which are very small. Fewer than 50 firms employ more than 1,200 people.

Introduction
3
Only 100 have more than 600 employees, so construction is often called a fragmented industry, and this is
the situation in most of the countries of the world.These firms are located all over the UK; everyone
has their local builders, plumbers, joiners, etc. One of the main reasons for the large number of small firms
is that the barriers to entry to the industry are so low as to be virtually non-existent. By this we mean that
little capital is required to begin.A skilled (or in some cases, unskilled!) bricklayer or roofer can set himself
up in business very easily.The result is that every week in the construction industry in the UK, scores of
firms cease trading, while new firms are started every week.
Another reason for the presence everywhere of construction firms is that unlike the products of the
manufacturing industry, buildings are erected in a particular place; they cannot, in general, be built and
transported. Because of this everyone needs their local builder.
Because the industry is so large, it is therefore a huge consumer of materials, both in the UK and
worldwide. In fact, it is the largest consumer of materials in the UK and worldwide by a considerable
margin.The total weight of materials consumed by all other industries combined is barely a quarter of that
used in construction.The consequence of this is twofold:first,our use of construction materials has a major
impact on our environment; and second, it is of the utmost importance that these materials are used
correctly and as efficiently as possible.
Construction uses a wider range of materials than any other. Materials used include cement and
aggregates to make concrete,metals – primarily steel,but with significant amounts of copper,copper alloys
and aluminium alloys – timber,fired clay products,glass,gypsum products,polymers,bituminous materials,
etc.The global consumption of the principal materials is shown in Table 1.1.
The table shows the proportion of these materials going to construction. It does not include fired clay
products, which are widely used in construction, because global figures for this material are difficult to
obtain. Such materials are not used in significant amounts by the other industrial sectors.
For comparison, the automotive industry consumes just 15 per cent of the world’s steel output, a total
of just over 200,000,000 tonnes. Steel is the principal material of the car makers, and the other materials it
uses are 40 per cent of the world’s rubber and 25 per cent of the world’s glass output. So automobile
production uses a tiny fraction of the quantities used in construction, and the aerospace business uses less
still.The two major constructors of large passenger aircraft, Boeing (US) and Airbus Industrie (Europe),
each deliver between 300 and 500 planes per year, depending upon the economic climate. If the average
weight of each plane is 250 tonnes, this gives a total material consumption of 250,000 tonnes in a good
year. Globally, the annual consumption of materials in the aircraft business is therefore under 1,000,000
tonnes. However, these materials will be very high value, with aero-engine materials in particular costing
up to £1,000,000 per tonne.
The shipbuilding industry is another large consumer of material; steel is the one used in the greatest
amounts. The present size of the world’s merchant fleet stands at 1.0 billion tonnes dead-weight,
and comprises just under 43,000 vessels. For the purposes of these statistics, a merchant ship must be over
Table 1.1 World production of principal materials, and the approximate proportion going to the construction
industry
Material Annual world production (tonnes) % of world production used in construction
Cement 2,400,000,000 95–100
Aggregates 12,000,000,000 95–100
Steel 1,450,000,000 Up to 50
Timber 1,000,000,000 c.60
Polymers 150,000,000 c.20–25
Total 17,000,000,000

4
Introduction
70 m long (about 230 feet).This tonnage is being added to at the rate of nearly 100,000,000 tonnes per
year,with China now being the largest constructor.These ﬁgures do not include naval construction,or the
construction of smaller vessels of less than 70 m length.The consumption of steel in shipbuilding may
therefore be taken as between 150,000,000 and 200,000,000 tonnes per annum.Table 1.2 compares the
approximate amounts of material consumed annually by construction, shipbuilding, automobile
manufacture and aircraft production.
Of course, steel is also used in agriculture, white goods manufacture, machine tools, etc. But Table 1.2
shows the predominance of construction in material consumption.
Finally, all industries have used more and more materials as the years go by, i.e. the production and
consumption graphs are all climbing with time.However,in the developed world,more materials are going
into buildings as a proportion of the total than ever before (see Figure 1.1). Figure 1.1 gives data for the
United States, but the pattern is the same all over the developed world.
The graphs shown in Figure 1.1 are very interesting. We can see that consumption of all classes of
materials increased during the 100 years from 1900 to 2000.The peaks caused by theWorldWars, and the
Table 1.2 Approximate global annual consumption of materials by construction, shipbuilding, automobile and
aircraft production
Industry Annual consumption of materials (tonnes)
Construction At least 10,000,000,000
Shipbuilding At least 500,000,000
Automobiles Around 400,000,000
Aircraft Under 1,000,000
1900
3,500
3,000 Construction materials
3,000
2,500
2,000
1,500
1,000
500
0
2,500
2,000
1,500
1,000
500
0
1910 1920 1930 1940 1950 1960 1970 1980 1990 1995 2000
Year
Millions
of
metric
tons
Millions
of
metric
tons
Industrial materials
Metals
Nonrenewable organics
Agricultural and forestry products
Great
Depression
WW I
WW II
Figure 1.1 Consumption trends of various materials by the United States for the twentieth century
(Source: United States Geological Survey)

Introduction
5
troughs occasioned by the Great Depression of the early 1930s, and the mid 1970s and 1980 oil crises are
clearly visible. However, two features are noteworthy: (1) the increase in consumption of materials for
construction far outstrips all other classes of materials,and (2) economic recessions have a disproportionately
large effect on the construction industry.The data are for the United States,but the same trends are widely
observed across the rest of the world. In short, this graph illustrates the pre-eminent importance of
construction and its consumption of materials, and this theme will be returned to in the final chapter
of this book.
1.2.1 Brief history of building materials
The finding and provision of shelter is one of the most basic human needs. When homo sapiens
first appeared on Earth, they existed as hunter-gatherers, and would find shelter in caves and other
convenient natural features.Around 8000 bc,however,mankind began to make the transition from hunter-
gatherer to farmer, and men ceased to be nomadic and settled on their farmland. The need to build
permanent settlements on their land became a major concern, and this step initiated the development of
man as a building constructor. At this time, the population of the Earth would be perhaps 20,000,000
people in all. Once the human population density reached more than two people per square mile, the
hunter-gatherer lifestyle was no longer sustainable,and more intensive methods for providing food became
imperative.
In building his shelter man would utilise the materials that came to hand locally, such as timber, stone,
animal skins and bone, etc.The mastery and use of fire led to the discoveries of ceramics, including fired
clay, glass and also the smelting of metals. As millennium followed millennium, men discovered how to
utilise a gradually increasing array of materials. So important were the materials used by men that the
ages of mankind’s development were named after the materials used, i.e. Stone Age, Bronze Age, Iron Age,
and so on.
The Industrial Revolution, beginning at the start of the eighteenth century, initiated an acceleration in
the pace of discovery and technological development, so that by the end of the nineteenth century, man
had perhaps 100 or so materials at his disposal to meet all of his needs.The twentieth century saw the
acceleration become an explosion in the number of available materials;Ashby (1992) has suggested that we
now have between 40,000 and 80,000 different materials from which to choose.
The balance between types of materials has changed dramatically over time. In early historical times
(10000 bc onwards) ceramics and glasses were important, together with the use of natural polymers and
elastomers, and early composites such as straw-reinforced bricks and paper.The use of metals was known,
but only a few metals had been identified – gold and copper being two of the earliest. By the middle of
the twentieth century, metals had become the single most important class of materials. Since that time
discoveries in the fields of polymer and ceramics have redressed that balance, and developments of
engineering composites have also had a major impact. Figure 1.2 illustrates the balance between the
various material types over time. It is important to recognise that the figure shows relative importance of
the various material types and not absolute amounts.For example,at the start of the twentieth century,the
total annual consumption of materials was well under one billion tonnes, whereas now it runs at over
16–17 billion tonnes.
However,the need for shelter is just as important as it ever was;this is true for all peoples in all countries.
The construction industry has grown and developed to meet this need, and as a result it is the largest
industry in the UK and in the rest of the world.This industry is the largest consumer of materials by far,
as well as using a much wider range of material types than any other.The manufacture and use of all this
material has an enormous impact on our world, which is our natural environment.This whole area of
environmental impact and sustainability is a matter of increasing concern; we shall need to say something
about this, and this discussion will be found in the last chapter of this book.

2020
2010
2000
1990
1980
1960
1940
Date
Relative
Importance
1900
1800
1500
1000
0
5000
BC
STONE
STRAW-BRICK
PAPER
WOOD
GOLD
COPPER
BRONZE
IRON
CAST
IRON
STEELS
ALLOY
STEELS
LIGHT
ALLOYS
SUPER
ALLOYS
GLASSY
METALS
AL-LITHIUM
ALLOYS
DUAL
PHASE
STEELS
MICROALLOYED
STEELS
NEW
SUPER
ALLOYS
DEVELOPMENT
SLOW:
MOSTLY
QUALITY
CONTROL
AND
PROCESSING
SKINS
FIBRES
GLUES
RUBBER
BAKELITE
NYLON
PE
PMMA
PC
PS
EPOXIES
POLYESTERS
HIGH
MODULUS
POLYMERS
HIGH
TEMPERATURE
POLYMERS
CERAMIC
COMPOSITES
METAL-MATRIX
COMPOSITES
KEVLAR-FRP
CFRP
CFRP
ACRYLICS
PP
FLINT
POTTERY
GLASS
CEMENT
REFRACTORIES
PORTLAND
CEMENT
FUSED
SILICA
CERMETS
PYRO
CERAMICS
TOUGH
ENGINEERING
CERAMICS
(Al
2
O
3
,
Si
3
N
4
,
PSZ
etc)
10000
BC
NFA
86
2020
2010
2000
1990
1980
1960
1940
1900
1800
1500
1000
0
5000
BC
10000
BC
TITANIUM
ZIRCONIUM
ETC
ALLOYS
METALS
POLYMERS,
ELASTOMERS
POLYMERS,
ELASTOMERS
CERAMICS,
GLASSES
CERAMICS,
GLASSES
METALS
COMPOSITES
COMPOSITES
Figure
1.2
The
evolution
of
engineering
materials
(After
Ashby,
1992)

Introduction
7
1.2.2 The materials of construction
A wider range of materials are used in building construction than any other branch of industry.This range
includes steel and certain other non-ferrous metals, cement, concrete, plaster, clay bricks and tiles, timber,
glass, polymers, bituminous materials, natural stone, etc. For convenience, we shall classify these materials
in three groupings:
1 metals, ferrous and non-ferrous
2 ceramics and other inorganic materials
3 polymers and natural organic materials.
It will be necessary to spend a little time on some of the underlying scientific principles governing the
behaviour of materials.We need to appreciate the reasons why metals used in construction such as steel,
lead and copper are ductile, and concrete and bricks, for example, are not.
1.3 Properties of materials
When a builder, architect or engineer specifies a material, he or she is really specifying a property or
combination of properties.Materials are used for the properties that they possess,whether it be compressive
strength, thermal insulation, high electrical conductivity, appearance, low cost or whatever.The properties
that materials possess derive from their structures, i.e. the way that their component atoms and molecules
are put together.This book does not set out to be a physics, chemistry or engineering text, but we require
a little insight into the structures of materials if we are to understand how they perform in service.
It is worth bearing in mind that when we use a material,as was pointed out earlier,we are really making
use of its properties. For this reason it will be a valuable exercise to look next at the process of selecting
materials.This is not something usually covered in books on construction materials; the topic has rather
been the subject of texts produced for engineers. However, materials selection will be dealt with as part of
Chapter 18, under the heading of rational selection methods.
However, it will be useful to take a preliminary look at the range of properties we have at our disposal,
and it is illuminating to consider properties by material classes such as ceramics, metals, polymers and
composites. Such is the very wide range of property values that the values have to be plotted on a
logarithmic scale. Figure 1.3 compares values of yield strength vy
for ceramic, metallic, polymeric and
composite materials.We can immediately see that ceramics have very much higher strengths than polymers,
while metals have a much wider range of strengths, from alloy steels down to some very soft, pure metals.
Similar wide variations are seen for stiffness values (E), in Figure 1.4, and for density (t), in Figure 1.5.
Note the very wide variation in properties shown in Figure 1.3. The strength covers six orders
of magnitude, i.e. the highest value (diamond) is nearly one million times stronger than the lowest
(foamed polymer).
In Figure 1.4, again note the wide variation in stiffness values, with the data spanning six orders
of magnitude. The stiffest material (diamond) is a million times stiffer than the least stiff material
(foamed polymer).
Density values shown in Figure 1.5 span three orders of magnitude, with the densest metals
(platinum and tungsten) being about 1000 times more dense than the lightest (foamed polymers).
1.4 Behaviour of materials in service
We shall consider the conditions under which materials serve in buildings,including the loadings to which
they are subjected and the environmental influences which surround them.This is very important because
we need to be as economical with materials, which are precious resources, as we can.

8
Introduction
Diamond
SIC
Si3
N4
Silica glass
Al2
O3
, WC
TiC, ZrC
Sodo glass
MgO
Alkali
halides
Ice
Ceramics
105
103
103
102
101
1
0.1
σγ/MN
m
–2
Cement (non-
reinforced
Low-alloy steels
Cobalt alloys
Nimonics
Stainless steels
Tl alloys
Cu alloys
Mid steel
Al alloys
Metals
Drawn PE
Drawn nylon
Kevla
Polyurethane
PMMA
Nylon
Epoxies
P.S.
P.P
Polymers
BFRP
Composites
CRFP
Reinforced
concrete
Woods, II
grain
Woods, I
grain
CRFP
Polyethylene
Foamed
polymers
Commercially
pure metals
Lead alloys
Ultra-pure
metals
Figure 1.3 Bar chart of data for yield strength, vy
(MN/m2
)
(After Ashby & Jones, 1980)
In service, we are nearly always concerned with the durability of our materials. Unlike motor vehicles,
which have a life of perhaps a decade,buildings are usually expected to last considerably longer,and massive
repair and maintenance costs are not welcome to those who are responsible for them. Durability is the
term used to describe the robustness of materials in the face of the service conditions that they endure; in
simple terms, how long they last.
In Victorian times, mankind had perhaps 100 or so different materials which had to meet all of our
needs, and which were somewhat less than ideal for their application. Fortunately, most of those materials

Introduction
9
Diamond
WC, SIC
Al2
O3
, Si3
N4
MgO
ZrO2
Mullite
Silica
Soda glass
Alkali halides
Cement
Concrete
Graphite
Ice
Ceramics
103
102
101
1
10–1
10–2
10–3
E/GN
m
–2
Osmium
Tunsten
Molybdenum
Nickel
Iron + Steel
Copper
Titanium
Aluminium
Zinc
Tin
Magnesium
Lead
Metals
Alkyds
Upper limit
Cements
CFRPs
Fibreglass
GFRPs
Woods, II
grain
Melamines
Polyimides
PMMA
Polystyrene
Nylon
Epoxy
(High density)
Polyethylene
(Low density)
Polypropylene
Rubbers
PVC
Foamed
polymers
Polymers Composites
Woods, I
grain
Figure 1.4 Bar chart of data for Young’s modulus, E (GN/m2
)
were tolerant of abuse, and while not totally suited to their use nevertheless performed adequately.
We are much more fortunate today, in the twenty-ﬁrst century, in having a very much greater number of
available materials, including composites, so that we can select materials having optimal properties for the
particular application that we wish to fulﬁl.
An important part of this book will be to deal with how the various materials perform in
service,together with the ways in which they can fail.We need to appreciate the environmental conditions
in which the materials serve, as well as the types of events they may encounter or endure during their
service lives.

10
Introduction
WC
TiC
ZrC
Ice
Ceramics
10–3
102
50
5×102
103
104
3×102
5×103
3×103
3×104
ρ/kg
m
–3
Platinum
Tungsten
Gold
Lead
Silver
Copper,
Nickel
Iron, Steels
Zinc
Titanium
Aluminium
Beryllium
Metals
PTFE
PVC
Epoxies
PMMA
Nylon
Polystyrene
Polyethylene
Rubbers
Cements
GFRPs
CFRPs
Foamed
polymers
Polymers Composites
Al2
O3
, MgO
Si3
N4
, SiC
Alkali halides
Most rocks
Glass
Cement/
Concrete
Common
woods
Figure 1.5 Bar chart of data for density, t (kg/m3
)
In the ﬁrst place, buildings stand, apparently doing nothing, and are subject to the elements of the
weather,and local meteorological conditions.On a day-to-day basis,this includes variations in temperature,
precipitation and humidity, and wind conditions. If the building is in an urban location, vibrations from
vehicular trafﬁc may be a factor.The temperature may fall below 0 °C from time to time, and this can
pose serious problems if water has been absorbed into cracks in structures or into individual materials.
On freezing, water undergoes a 9 per cent volume increase, and this can cause stressing and cracking of
those material which are inherently brittle.

Introduction
11
This fact raises another very important factor in material performance, and that is the subject of
porosity in materials. Some materials are porous, such as clay bricks, concrete and timber. Others are fully
dense and impermeable to water. Such materials include metals, sheet plastics, glass, etc.The porosity will
determine whether water will be absorbed by materials during service or not. Porosity will also be a
determinant of the mechanical properties of materials, as we shall see. The phenomenon of capillarity
means that porous materials can absorb water when they are exposed to it, and also tend to retain it even
when the surplus water has drained from their surfaces.The water does not always have to be in liquid
form, porous materials containing moisture will equilibrate with their surroundings and absorb moisture
from the atmosphere during times when the weather is wet or humid. Similarly, they will then dry out
when the weather is dry or less humid.These effects cause expansion and contraction effects in addition
to those caused by temperature variations.
Another factor that is sometimes overlooked is that although buildings are static structures, they are
always under stress.A very large building will possess an enormous weight, and this load is carried by the
structural elements and foundations. For example, the Empire State Building in New York weighs over
300,000 tonnes.The stresses induced will be mainly compressive and monotonic. However, we need to
bear in mind that while the weight will be responsible for the so-called dead loads on the structure, there
will also be the live loads, i.e. those that are continuously varying from hour to hour and day to day.
The live loads will include loads due to wind pressure, varying occupancy, etc. In bridge structures some
of the stresses can be tensile in nature.
If the stresses vary in a cyclical way with time, they can lead to fatigue in metallic structural elements.
Such conditions can occur in bridge structures,and several historically famous bridge failures have occurred
because of fatigue.
However, even simple monotonic compressive stress can cause problems with some materials. Under
such conditions,the phenomenon of creep can occur.Creep can occur in many types of materials including
metals, concrete, polymers, masonry, glass and timber. Some of the expensive mistakes made in the
construction of multi-storey tower blocks in the 1960s arose because creep and other relative movement
effects were not taken into account.We shall examine this later.
In addition to these routine environmental variations, we must also consider other events such as
fires, explosions and earthquakes. In the UK, fire is the commonest of these hazards. Explosions also
occur, though less frequently than fires. One of the most common causes of explosions is gas leaks
in domestic properties. Such explosions can be very destructive, often resulting in the partial or
complete demolition of the house in which the leak occurred. During such events, the materials
from which the building structure is made are subjected to rapid, dynamic loading, and the response of
materials to such loading can be markedly different from their response to gradually or more
slowly applied loads. This is also true for seismic activity. Fortunately, earthquakes are infrequent
and relatively minor events in the UK. In other parts of the world, building design codes are written
to take account of earthquakes, and the dynamic loading that they give rise to. In the UK, such
earthquakes as do occur are mid-plate phenomena, like the one that occurred in January 2008,
which measured 5.4 on the Richter scale.This was sufficient to cause only very minor damage to some
buildings.
1.4.1 The use of materials and their impact on the environment
Because at least three-quarters of the materials used on planet Earth go into buildings and infrastructure,
and because this is such a huge quantity, the manufacture, use and disposal of building materials has an
enormous impact on our environment. The consequences of their use include energy consumption,
pollutioneffectsinair,waterandsoil,despoliationoflandscapes,resourcedepletion,etc.,onacorrespondingly
large scale.Unless energetic steps are taken to minimise and mitigate these effects,there is a real danger that

12
Introduction
we shall leave a degraded world to our successors and descendants rather than one enhanced for its
occupants.
The impact that the use of materials has is not simple, and can have several ramifications. For example,
extraction of raw materials can lead to spoiling of the landscape, as also can the deposit of waste materials
from the production process.The production process can give rise to the emission of dust and gases into
the atmosphere, as well as waste liquids and other solids.We need ways of measuring or quantifying these
effects if we are to control these adverse impacts, and this question will be re-visited in the last chapter of
the book.This is a topic of considerable current importance, with concerns increasingly being expressed
about how sustainable our present mode of life will be in the long term.Unfortunately,the word sustainable
is now very widely used, and not always by people who understand what it might mean. In the serious
academic community, its meaning is still being debated and clarified.This topic will be dealt with in the
final chapter of this book.
1.5 The contents of this textbook
The construction industry uses a very wide range of materials, wider in fact than that used by any other
industry. Metals, ceramics, organics – natural and man-made – are used in enormous quantities. It is
important that these materials are used economically and efficiently and not wasted, as construction
materials in the past unfortunately have been (Anon, 1987). Waste is the hallmark of the present age.
Archaeologists and anthropologists learn a good deal about ancient civilisations by excavating their middens
and waste dumps.Archaeologists of the future (if they are still around) will be amazed at what our current
civilisation throws away! But in today’s increasingly environmentally conscious world, waste is belatedly
being seen for what it is – gross mismanagement of our planet’s resources.This theme will be taken up in
the final chapter of the book.
As far as the main body of the book is concerned, it falls into three sections:
1. Basic principles. First, the book will attempt to cover the basic science of the materials of construction.
The aim will be to give the minimum coverage to the principles governing the behaviour and
properties of these materials.This first section will also include a chapter on the basic principles of
structures, since many materials are used to build structures.
2. Individual materials and classes of materials.The second section will then deal in detail with the individual
types of materials and how they perform in service.It will therefore have something to say about how
construction materials in buildings degrade and fail.This section will build on the basic science of the
first section and will move on to deal with the individual types of material in turn.
3. Materials in service, durability and failure. The third section will deal with those issues arising when
materials are put into service, including different modes of failure, the effects of corrosion and solar
irradiation, the effects of stress and types of fracture, and the effects of fire, etc.
Finally, since construction is by far the largest industry globally and the largest consumer of materials, and
given the current preoccupation with sustainability, the enormous impact that construction has on our
environment will be dealt with in the concluding chapter.
1.6 Critical thinking
The aim of this section is to provide the student with the opportunity to reflect on what he/she has
learned, and to think about some of the main ideas outlined in the chapter. Questions for thought will be
outlined in a critical thinking box,and other questions will be set out for students to work through,to help
their understanding of important sections of the text.

Introduction
13
1.7 Concept review
1 Construction materials are, in the main, inexpensive and low-tech. Explain why they are considered
to be so important in the world of the twenty-ﬁrst century.
2. Why are steel and concrete two of the most important materials of construction?
3. List the principal materials of construction. Which of these materials are porous and which are
impermeable?
4. Why is porosity such an important factor in determining the behaviour of construction materials?
5. What, in general, is the link between the cost of a material and how much of that material is used?
1.8 References and further reading
ANON. (1987), Materials for Construction and Building in the UK,The Materials Forum and The Institution of Civil
Engineers,The Institute of Metals, London.
ASHBY, M.F. (1992), Materials Selection in Mechanical Design, Pergamon Press, Oxford.
ASHBY, M.F. and JONES. D.R.H. (1980), Engineering Materials: An Introduction to their Properties and Applications,
Pergamon Press, Oxford.
COLE,R.J.(1999),Building EnvironmentalAssessment Methods:Clarifying Intentions,Building Research & Information,
Vol. 27 (4/5), pp. 230–246.
GREENMAN, D. (ed.) (2008) Jane’s Merchant Ships 2008, Jane’s Information Group
HARVEY, R,C. and ASHWORTH,A. (1997), The Construction Industry of Great Britain, 2nd edition, Laxton’s, Oxford.
McKINNEY, M.L., SCHOCH, R.M. and YONAVJAK, L. (2007), Environmental Science: Systems and Solutions,
4th edition, Jones and Bartlett Publishers, Sudbury, MA.

Part I
Basic principles:
material structures and properties

17
2
Bonding and structures
Contents
2.1 Fundamentals and structure of the atom 17
2.2 The periodic table 18
2.3 Bonding 18
2.3.1 Bond strength and material properties 21
2.3.2 Ionic bonding 21
2.3.3 Covalent bonding 21
2.3.4 Metallic bonding 22
2.3.5 van der Waals and hydrogen bonding 23
2.4 Crystal structures 24
2.5 Polymorphism and allotropy 26
2.6 X-ray diffraction 27
2.7 Critical thinking and concept review 27
2.1 Fundamentals and the structure of the atom
The idea that matter is made up of small, discrete particles is a very old one. Such a scheme was described
by Democritus (460–370 bc) over 2,000 years ago.The modern notion of the atom was put forward by
the English chemist John Dalton in 1800. He envisaged atoms as small, indivisible particles, with the atom
being the smallest quantity of an element obtainable that retains the properties of that element.We now
know that atoms are not indivisible, but they consist of smaller sub-atomic particles, protons, neutrons and
electrons. Indeed, modern research in high-energy physics has shown that these particles can be broken
down even further, but for our purposes an atom is most easily visualised as a nucleus surrounded by
orbiting electrons. The nucleus contains most of the mass of the atom, and consists of neutrons (large,
electrically neutral particles) and protons (large, positively charged particles). The orbiting electrons are
negatively charged, and are tiny compared to the nuclear particles.The number of protons in the nucleus
deﬁnes which element it is, and this number is called the atomic number Z.Table 2.1 shows the relative
masses and charges of these three types of particle.

18
Basic principles
In a stable atom, the number of protons and electrons will be equal, and so overall the atom will carry
no charge. However, as we shall see later, atoms can both lose and gain electrons. If they do this they are
said to become ionised; gaining an electron will make them into a negatively charged ion (also known as
an anion),losing an electron will result in them becoming a positively charged ion (also known as a cation).
2.2 The periodic table
In 1869 the Russian chemist Dmitri Mendeleev first noted that the chemical elements exhibited a
‘periodicity of properties’. He had tried to organise the chemical elements according to their increasing
atomic weights. He had assumed that their properties would progressively change as their atomic weights
increased, but he found that their properties changed and then seemed to be repeated at sudden distinct
steps, so that they could be arranged or grouped into distinct periods. One of his particular insights was
that in 1869 there were elements that remained undiscovered, and which would, when found, occupy the
missing places in his periodic scheme.This insight enabled him to predict accurately many of the properties
that that an element was found to possess when it was isolated later. For example, he gave the name eka-
silicon to the element germanium,which had not yet been discovered in 1869,and he successfully predicted
several of its properties.
The modern periodic table of the elements is shown in Figure 2.1,and is based upon Mendeleev’s ideas.
It is organised by atomic number Z, and not by atomic weight.As we move from left to right along a row
or period,the properties of the elements gradually change.The last element in each row is chemically inert,
i.e.helium,neon,argon,krypton,xenon,radon – these are the inert gases.Those to their immediate left are
the very reactive halogens, i.e. fluorine, chlorine, bromine, iodine, astatine. Their reactivity or inertness
results from their outer electronic structures, as we shall see later.Therefore the elements in any column
(called groups) tend to possess similar chemical properties.The periodic table has enormous significance in
understanding the chemical behaviour of the elements, because it is rooted in their atomic numbers and
therefore in their electronic structures.
At this point it is appropriate to point out that of the 100 or more elements in the periodic table,three-
quarters are metals.Some of these,such as the rare earth metals,are found in nature in tiny amounts.In this
modern age of electronic goods, some of these metals have become of great technological importance,
despite being used in tiny amounts.The world annual production of many of these metals is often only a
few hundred tonnes in total.
2.3 Bonding
We have looked briefly at the properties of atoms, but in practice our materials are made up of assemblies
of atoms arranged in a myriad different ways, and we must now examine the various ways in which they
can be bonded together.We shall see that it is the outer electronic structure of the atoms that is responsible
for the bonding, and not the nuclear cores.We shall also see that it is the qualities of these bonds that
determine the properties of our materials. By properties we mean principally the mechanical, thermal and
electrical properties of materials.
Table 2.1 Relative masses and charges carried by atomic component particles
Particle Mass Charge
Neutron 1,840 Zero
Proton 1,836 +1
Electron 1 –1

nitrogen
14.007
N
7
helium
He4.0026
2
neon
Ne20.180
10
fluorine
F18.998
9
oxygen
O15.999
8
carbon
C12.011
6
boron
B10.811
5
argon
Ar39.948
18
chlorine
Cl35.453
17
sulfur
S32.065
16
phosphorus
P30.974
15
silicon
Si28.086
14
aluminium
Al26.982
13
krypton
Kr83.798
36
bromine
Br79.904
35
selenium
Se78.96
34
arsenic
As74.922
33
germanium
Ge72.64
32
gallium
Ga69.723
31
zinc
Zn65.38
30
copper
Cu63.546
29
nickel
Ni58.693
28
cobalt
Co58.933
27
iron
Fe55.845
26
manganese
Mn54.938
25
chromium
Cr51.996
24
vanadium
V50.942
23
titanium
Ti47.867
22
scandium
Sc44.956
21
calcium
Ca40.078
20
potassium
K39.098
19
magnesium
Mg24.305
12
sodium
Na22.990
11
beryllium
Be9.0122
4
lithium
Li6.941
3
hydrogen
H1.0079
1
xenon
Xe131.29
54
iodine
I126.90
53
tellurium
Te127.60
52
antimony
Sb121.76
51
tin
Sn118.71
50
indium
In114.82
49
cadmium
Cd112.41
48
silver
Ag107.87
47
palladium
Pd106.42
46
rhodium
Rh102.91
45
ruthenium
Ru101.07
44
technetium
Tc[98]
43
molybdenum
Mo95.96
42
niobium
Nb92.906
41
zirconium
Zr91.224
40
yttrium
Y88.906
39
strontium
Sr87.62
38
rubidium
Rb85.468
37
radon
Rn[222]
86
astatine
At[210]
85
polonium
Po[209]
84
bismuth
Bi208.98
83
lead
Pb207.2
82
dysprosium
Dy162.50
66
terbium
Tb158.93
65
gadolinium
Gd157.25
64
europium
Eu151.96
63
samarium
Sm150.36
62
promethium
Pm[145]
61
neodymium
Nd144.24
60
praseodymium
Pr140.91
59
cerium
Ce140.12
58
lanthanum
La138.91
57
barium
Ba137.33
56
caesium
Cs132.91
55
unununium
Uuu[272]
111
ununquadium
Uuq[289]
114
ununbium
Uub[277]
112
ununnilium
Uun[271]
110
meitnerium
Mt[268]
109
hassium
Hs[277]
108
bohrium
Bh[264]
107
seaborgium
Sg[266]
106
dubnium
Db[262]
105
rutherfordium
Rf[261]
104
radium
Ra[226]
88
francium
Fr[223]
87
lutetium
Lu174.97
71
ytterbium
Yb173.05
70
thulium
Tm168.93
69
erbium
Er167.26
68
holmium
Ho164.93
67
thallium
Tl204.38
81
mercury
Hg200.59
80
gold
Au196.97
79
platinum
Pt195.08
78
iridium
Ir192.22
77
osmium
Os190.23
76
rhenium
Re186.21
75
tungsten
W183.84
74
tantalum
Ta180.95
73
hafnium
Hf178.49
72
berkelium
Bk[247]
97
lawrencium
Lr[262]
103
nobelium
No[259]
102
mendelevium
Md[258]
101
fermium
Fm[257]
100
einsteinium
Es[252]
99
californium
Cf[251]
98
curium
Cm[247]
96
americium
Am[243]
95
plutonium
Pu[244]
94
neptunium
Np[237]
93
uranium
U238.03
92
protactinium
Pa231.04
91
thorium
Th232.04
90
actinium
Ac[227]
89
Figure
2.1
The
periodic
table
of
the
elements

20
Basic principles
Bonding is the name given to the mechanism by which two (or more) atoms join together to form
compounds.There are several types of primary bond that can be formed, and these are all determined by
the extra-nuclear or electronic make-up of the elements. It is the electrons, and not the nuclei, that form
the various types of bond. Furthermore, these bond types can vary widely in their strengths; the energy
required to separate two bonded atoms is the bond energy, and this governs not only mechanical strength
but also other properties such as melting temperature.An element or compound with a high bond strength
will be more difﬁcult to melt, i.e. it will tend to have a higher melting temperature. It will also have a
higher value of stiffness (Young’s modulus of elasticity, E).
Before we look in more detail at the various kinds of chemical bonding that are commonly found, it
will be proﬁtable to consider the cohesive forces that hold atoms together and the binding energies
involved.These considerations apply to the forces of attraction between any pairs of atoms or molecules,
be they in the gaseous, liquid or solid states. In Chapter 6 we shall consider thermal properties, but it is
worth pointing out here that heat is atoms and molecules in motion. In solids, the atoms or molecules
vibrate or‘wriggle’about a mean position;in liquids they move randomly around inside the liquid,colliding
with each other from time to time; in gases the atoms and molecules move with greatest speed, and move
around randomly within whatever space is available to them.
In any group of atoms or molecules, be they gas, liquid or solid, there will be short-range forces of
attraction operating.These can be represented by curve 1 in Figure 2.2.There will also be strong, short-
range forces of repulsion that operate to resist compression when the atoms or molecules come into close
proximity, and these are represented by curve 2 in Figure 2.2. If these curves (forces) are added we obtain
a resultant force, curve 3.We can see that this resultant gives a position of stability at a spacing of a0
; any
deviation from this spacing will be opposed by a restoring force, either tensile of compressive. Curve 4
shows that the system has minimum energy with this zero-force spacing, and will therefore be in
+
0
–
Energy
0
Force
Repulsion
Attraction
Distance between centres
1
3
2
4
φ0
α
0
Figure 2.2 Forces and energy of interaction between particles
(After Cottrell, 1964)

21
equilibrium. It can be seen that this resultant curve 3 is the same as the important curve shown in
Figure 3.2 in Chapter 3.
2.3.1 Bond strength and material properties
As has been mentioned above, the strength of the bonds between atoms has a major inﬂuence on the
properties of the solids made up of these atoms.This is quite logical,as the phenomena of elastic deformation,
fracture and melting all involve the pulling apart of atoms in solids. So we would expect to see materials
having high strengths also being difﬁcult to melt (high melting temperatures) and having high stiffness
values. In fact, there is such a link between these properties, and this is illustrated in Table 2.1.This table
gives properties for diamond (a covalently bonded solid) and six metals, and from it we can see that ionic
and metallic bonding can give rise to strong bonds.
The bonding mechanisms all involve electron donation from one atom to another, or electron
sharing in some form,or electrostatic attraction brought about by electron gain or loss.There are a number
of primary (strong) bond types, the most common being ionic, covalent and metallic. Secondary (weak)
bonds include van der Waals and hydrogen bonds, which we shall now examine in turn.
2.3.2 Ionic bonding
This is the simplest type of bond. It has been pointed out above that halogen atoms are very reactive.This
is due to the fact that when an atom has an outer set of electron orbits (known as a ‘shell’) which is full,
bonding will not happen.If the atom has an outer shell that lacks one electron,then it will be keen to gain
one more, and it is this fact that makes the halogens so reactive as a group.
On the left-hand side of the periodic table are the alkaline metals – lithium, sodium, potassium, etc.
These metals have just one electron in their outer shell.Therefore, by donating an electron to a halogen,
an ionic or electrovalent bond is formed. Consider the case of sodium chloride. The donation of an
electron by the sodium atom produces a positively charged sodium ion (Na+
) while the donation
of an electron to a chlorine atom produces a negatively charged chloride ion (Cl–
). So the charged ions
form a so-called ionic bond.
2.3.3 Covalent bonding
This is a very common type of bond; it is found in most polymeric type materials, and it involves electron
sharing.We have already looked at chlorine,one of the halogens.Chlorine forms a stable diatomic molecule
Table 2.1 Showing values of strength, stiffness (Young’s modulus) and melting temperature for a range of
elements
Element Yield strength
(MPa)
Stiffness (E)
(GPa)
Melting/softening
temperature
Diamond 50,000 1,000 3,800
Tungsten 6,000 450–650 3,380
Steel 0.4%C 400 200 1,450
Iron 50 196 1,537
Copper 60 124 1,083
Aluminium 40 69 660
Lead 11 14 327

22
Basic principles
Figure 2.3 Schematic representation of ionic bonding
(After Smallman & Bishop, 1995)
(Cl2
) by each of the two chlorine atoms donating one electron to give a pair, which are then shared.This
is the so-called covalent bond.
There is another variation on the covalent bond – the coordinate covalent bond.In this case,one of the
atoms that are bonded together donates both of the shared electrons. One important characteristic of
covalent bonds is that they can be very strong; the bonding between the carbon atoms in diamond is
covalent. Diamond is a very strong solid, with a high stiffness (high value of Young’s modulus E), and a
high melting temperature.All of these properties result from a high value of bond strength.The bonding
in many polymers is also covalent – mountain climbers trust their lives to nylon climbing ropes!
2.3.4 Metallic bonding
We have seen that metals are the largest group of elements in the periodic table, and metallic bonding is
the name given to the bonds formed when metal atoms aggregate together to form solid pieces of metal.
Metallic bonding is different from both ionic and covalent bonding. Metals have crystalline structures, and
to form bonds each metal atom loses its outer electrons to form cations, i.e. positively charged ions.The
free electrons from all the metal atoms thereby form a ‘sea’ of electrons, which can ﬂow around these
cations and through the lattice.These electrons are sometimes called ‘de-localised electrons’, because they
are not conﬁned to one place or freedom of mobility.This arrangement is illustrated in Figure 2.5.
The cations are all positively charged, and they will be subject to forces of attraction and also to forces
of repulsion (their positive charges will form part of the repulsive force).The atoms will take up constant
Figure 2.4 Schematic representation of covalent bonding

23
spacings from each other, and the distance apart will be the distance at which the attractive and repulsive
forces are exactly equal.As we shall see, it is these forces that give the metal its elastic properties.
The‘sea’of electrons,coupled with the regular electrical periodicity,is what gives metals their excellent
electrical conductivity properties. Finally, because all the atoms are lined up in a regular array, they are
ideally positioned for the easy and rapid transmission of heat energy. So their crystalline structure confers
on metals their excellent thermal conductivity properties as well.
2.3.5 van der Waals and hydrogen bonding
Whenever atoms are in close proximity to each other, they will attract each other by weak electrostatic
forces.These forces are seen even between chemically inert atoms like the inert gases.They are called van
derWaals forces and they are much weaker than ionic or covalent forces.They are very short-range forces,
and they exist between all atoms and molecules,regardless of whatever other forces may be involved.These
forces are caused by the fact that, even though the average electrical field of a neutral, spherical atom is
zero, its instantaneous field is not zero.This is due to the fact that the electrons within the atom will move
and cause the field to fluctuate. If the electrons in one atom move and leave the positively charged nucleus
somewhat exposed to the electrons in a second atom, the atoms are able to correlate their electronic
movements so that they are attracted to each other, and so form a weak van der Waals bond.
Metal ions
‘Gas’ of
‘free’ electrons
Figure 2.5 Schematic representation of metallic bonding
Figure 2.6 Schematic representation of van der Waals bonding

24
Basic principles
Such van der Waals bonding causes inert gases to liquefy, and later in this book we shall examine the
structures and behaviour of polymeric materials.Thermoplastics are of great technological importance,and
we shall see that they consist of long carbon chain molecules where the bonding is strongly covalent.
Strong, covalently bonded structures can be brittle. Nevertheless, thermoplastics are ductile. While the
carbon–carbon bonds along each molecule are covalent, van der Waals bonds form between the chains.
When thermoplastics are stressed to the point where they deform, these van der Waals bonds are broken
and the carbon chains slide past each other, thereby allowing the materials to change shape.
2.4 Crystal structures
Solid materials can be classiﬁed according to the regularity or otherwise with which their atoms and ions
are arranged relative to one another. Crystal structures are highly ordered; the state is characterised by a
regular, periodic three-dimensional array of atoms, ions or molecules, and these crystalline solids have
properties that result from this high degree of internal order.Non-crystalline structures,on the other hand,
are those without such long-range atomic order. Such materials are variously described as amorphous,
glassy or vitreous, and these terms are usually used synonymously.
Metals are a very important class of materials, and one of their characteristics is that they are crystalline,
i.e. their atoms are arranged in very regular arrays. Metals therefore have some of the most highly ordered
structures of all materials. While there are 14 different possible atomic arrangements with crystalline
systems, most of the metals of common technological importance conform to one of the three simplest
arrangements shown in Figure 2.8.These three common arrangements are:
1. body-centred cubic (BCC)
2. face-centred cubic (FCC)
3. hexagonal close-packed (HCP).
2.4.1 Body-centred cubic
This crystal structure type is found among some common metals,such as ferritic steel,pure iron,chromium,
tungsten, etc.We can characterise the various crystal forms by their atomic packing factor (APF).
Hydrogen bond
H2
O
molecule
Oxygen atom
Hydrogen atom
Figure 2.7 Arrangement of water molecules in ice, showing hydrogen bonds

25
c
a
a) Body-centred
cubic
b) Face-centred
cubic
c) Hexagonal
close-packed
Figure 2.8 The three main metallic crystal structures, (a) BCC, (b) FCC, (c) HCP
(After Callister, 1994)
APF
Total volume of unit cell
Volume of atoms in a unit cell
=
With BCC metals the atomic packing factor is 0.67, i.e. 67 per cent of the unit cell volume is taken up by
the constituent atoms.
2.4.2 Face-centred cubic
This is the structure found in some of the common engineering metals such as austenitic steel,aluminium,
copper, gold, silver, nickel, etc. (see Table 2.2).With FCC metals, the atomic packing factor is 0.74.This
means that 74 per cent of the unit cell volume is taken up by the constituent atoms.We can see from the
APF ﬁgures that FCC metals are more close-packed than BCC metals.

26
Basic principles
2.4.3 Hexagonal close-packed
This is the third common structure type, and the common metals conforming to this type include zinc,
magnesium, cobalt and cadmium.The atomic packing factor for HCP metals is 0.74, so it is a truly close-
packed structure.
2.5 Polymorphism and allotropy
Polymorphism of a solid material refers to its ability to exist in more than one form of crystal structure.
The particular form the material adopts will depend upon the local conditions of temperature and pressure.
Polymorphism can occur in various types of substance, elements and compounds, and in organic and
inorganic materials. In elements it is called allotropy.
One familiar example is found in carbon, where graphite is the stable allotrope at ambient conditions,
and diamond is formed at extremely high temperatures and pressures. In metals, the allotropes of greatest
technological signiﬁcance are those occurring in iron. At room temperature, pure iron exists as a crystal
with a BCC structure (a-iron or ferrite), and above 910 °C it transforms instantaneously to an FCC
structure (c-iron or austenite). If heated up to 1,394 °C, the austenite reverts instantaneously to a
BCC structure (d-iron), before melting at 1,538 °C. Because the FCC arrangement is more close-packed
than the BCC arrangement, there is a slight volume reduction when the alpha to gamma transformation
occurs,and a corresponding expansion when the FCC structure reverts to the BCC at 1,394 °C.The alpha
to gamma transformation is of enormous technological signiﬁcance because austenite will dissolve around
100 times more carbon than ferrite. If austenitic steel is rapidly cooled, there is no time or energy for
the carbon atoms to diffuse, and so the carbon is trapped in solution, thus preventing the FCC structure
from transforming to BCC ferrite. Instead, a body-centred tetragonal structure called martensite is
produced.This is a non-equilibrium structure possessing very high hardness and strength, and it provides
the basis for the heat-treatment of steels.That steel can be hardened to a remarkable degree by producing
Table 2.2 Crystal structures for some commonly used metals
Metal Crystal structure Inter-atomic distance (nm) Atomic radius (nm)
Aluminium FCC 0.2862 0.1431
Cadmium HCP 0.2978 0.1489
Chromium BCC 0.2498 0.1249
Cobalt HCP 0.2496 0.1248
Copper FCC 0.1556 0.1278
Gold FCC 0.2882 0.1441
Iron(a) B.C.C 0.24824 0.12412
Iron(c) FCC 0.2540 0.1270
Lead FCC 0.3499 0.1750
Magnesium HCP 0.3209 0.1610
Molybdenum BCC 0.2720 0.1360
Nickel FCC 0.2491 0.1246
Platinum F.C.C 0.2774 0.1387
Silver FCC 0.2888 0.1444
Tantalum BCC 0.2858 0.1429
Titanium HCP/BCC 0.2876 0.1438
Tungsten BCC 0.2738 0.1369
Zinc HCP 0.2665 0.1390

27
non-equilibrium martensite by rapid cooling has been known for centuries, but it has only been under-
stood since the middle of the twentieth century. The ability to achieve an almost infinite variety of
combinations of hardness, strength and ductility in what is essentially the cheapest industrial alloy is the
reason for the fact that the various grades of steel comprise about 90 per cent of all metals and alloys used
each year. It is because steel is a material of such technological importance and is used in such large
quantities that a whole chapter is devoted to it later in this book (Chapter 8).
2.6 X-ray diffraction
Because X-rays have wavelengths of the same order of size as the inter-atomic spacing in metal crystals
(10–10
m), metals will cause diffraction effects in beams of X-rays which impinge upon them. This
effect was discovered by Friedrich and Knipping acting on the suggestion of Max von Laue at the end of
the nineteenth century. Later work by W.H. Bragg and W.L. Bragg (1913) related the lattice parameter
(atomic spacing) of a metal crystal to the wavelength of the X-rays used and the angle of diffraction in a
simple equation:
n.m = 2d.sini
where:
m = wavelength of the X-ray beam
d = atomic spacing of the diffracting planes
i = incident angle of X-ray beam to atomic plane
n = an integer
If a beam of X-rays strikes a plane of metal atoms at some angle i, then there will be a path difference
of 2d.sini, if the planes of atoms are separated by distance d. If the path difference for that particular
value of i is equal to the wavelength of the X-radiation, then constructive interference will occur, and the
radiation will be strongly reflected.For other values of i,the path difference will not be a whole wavelength,
and so destructive interference will occur and there will be no strong reflection.
Being crystalline, metals have some of the simplest structures, and X-ray diffraction techniques and the
Bragg equation proved to be a very powerful tool in elucidating their structures, and measuring both their
lattice parameters and crystal type.Much of this work on metals was done before and just after the Second
World War. However, it was quickly realised that X-ray diffraction was a very powerful technique and
could be developed and applied to determine the structures of many more complex non-metallic materials,
including organic (both natural and man-made) materials and of various ceramic materials.The technique
has indeed proved to be very effective; for example, 60 years ago it was used to help decipher the structure
of DNA, the genetic material at the heart of all living cells.
The inter-atomic spacings quoted in Table 2.2 were all determined using X-ray diffraction.
2.7 Critical thinking and concept review
1. What is the difference between the atomic weight of an element and its atomic number?
2. Explain what is meant by an ionic bond, and give an example of an ionically bonded solid.
3. Explain what is meant by a covalent bond, and give an example of a covalently bonded solid.
4. Describe the nature of the metallic bond.
5. Produce a sketch of each of the three main crystal arrangements in metals, and give an example of a
common metal having such a crystal structure, for each of the three main types.

28
Basic principles
H’
H”
H
M
P
dhkl
A
K
K
λ
A λ
θ
θ
20
Figure 2.9 Bragg’s law of diffraction: diffraction only occurs when the conditions of the Bragg equation
are met
(After Van Vlack, 1974)
6. Explain why each metal crystal has its own unique lattice parameter (i.e. inter-atomic spacing).
7. What is meant by the term polymorphism?
8. A piece of pure iron is heated up to its melting temperature.Explain the changes to its crystal structure
that occur as it is heated, and give the temperatures at which these changes occur.
9. Which crystal structure is the more close-packed, body-centred-cubic or face-centred-cubic?
10. In iron, which crystal form (BCC or FCC) will dissolve the most carbon?
2.8 References and further reading
ASNBY, M.F. and JONES, D.R.H. (1980) Engineering Materials: An Introduction to their Properties and Applications.
Pergamon, Oxford.
CALLISTER,W.D. (1994), Materials Science and Engineering:An Introduction, 3rd Edition, John Wiley, NewYork.
COTTRELL,A.H. (1964), The Mechanical Properties of Matter, John Wiley & Sons Inc., NewYork and London.
FRIEDRICH,W. and KNIPPING, P. (1912), Ann. Phys., 4, p. 971.
SMALLMAN, R.E. and BISHOP, R.J. (1995), Metals and Materials, Butterworth-Heinemann, Oxford.
TABOR, D. (1979), Gases, Liquids and Solids, Cambridge University Press, Cambridge.
VANVLACK, L.H. (1974). Materials Science for Engineers, Addison-Wesley, Reading, MA.

29
3
Dislocations, imperfections,
plastic flow and strengthening
mechanisms in metals
This chapter provides an outline of the crystalline structure of metals and explains, in terms of this
crystalline structure, how metals deform both elastically and plastically. Depending upon the temperature,
metals will contain a population of crystal defects, and it is these defects that make them capable of plastic
deformation. By controlling the number, size and type of these defects, the strength and ductility of metals
can be controlled to meet the requirements of many design situations.The presence of these crystal defects
also influences in a major way the final failure and fracture of metals.
Contents
3.1 Introduction 30
3.2 Crystalline structure of metals 30
3.2.1 Crystal structure of the common metals 31
3.2.2 Forces between atoms in crystals 32
3.3 Stress vs strain behaviour of metals 33
3.3.1 Crystal structure of steel 34
3.3.2 Elastic behaviour 34
3.3.3 The elastic modulus or stiffness – a fundamental property 36
3.3.4 Plastic behaviour 38
3.4 Defects in crystals 38
3.4.1 Crystal imperfections 39
3.4.2 Dislocations and plastic flow 40
3.4.3 Plastic deformation of metals 40
3.4.4 Effects of temperature on plastic flow 41
3.4.5 Polycrystalline aggregates 42
3.4.6 The importance of ductility in steel 43
3.4.7 Strengthening mechanisms in metals 43
3.5 Fracture behaviour in metals 44
3.5.1 Role of cracks in fracture 46
3.5.2 Creep 47
3.5.3 Fatigue 48

30
Basic principles
3.6 Electrical and thermal properties of metals 48
3.6.1 Electrical properties 49
3.6.2 Thermal properties 49
3.7 Critical thinking and concept review 49
3.1 Introduction
Metals are a group of materials of great technological importance in construction and in engineering
generally. Since the advent of the Industrial Revolution, the application and use of metals has had an
incalculable impact on our modern society.The most important and most used metal is steel, an alloy of
iron and carbon. Other metals used in construction are copper, lead, zinc and a number of alloys such as
brass, and small amounts of stainless steel. Metals have remarkable properties. For example, many of them
can be shaped into an amazing variety of shapes and sections by being plastically deformed.This capacity
for plastic deformation without suffering fracture is called ductility.A piece of steel 100 mm thick can be
rolled down into a very thin strip 0.1 mm thick, without failure. This illustrates the amazing ductility
possessed by metals as a group.If we tried to roll a piece of concrete or a brick in the same way,they would
not deform, but suffer brittle fracture.
Metals also offer us tensile strength, which few of the traditional materials like natural stone or ﬁred clay
possess. Because of this remarkable combination of tensile strength and ductility, we can create all types of
buildings and other structures that were not possible before the Industrial Revolution. Metals also offer
fracture toughness, a resistance to brittle fracture not found in natural stone, clay brick or concrete, and this
makes them indispensable in the design and construction of many large buildings.
Metals, and steel in particular, possess high values of stiffness, i.e. high values of elastic modulus, E.
The high value of Young’s modulus is one of the major advantages of steel as a structural material.
A metal’s elastic modulus is a fundamental property of the metal,and its physical basis lies in the crystalline
structure of the metal, and in the nature and strength of the bonds between the atoms in the metal’s
crystal lattices.
Metals also possess excellent electrical and thermal conductivities, particularly FCC metals (see below) such
as copper and aluminium.These are properties that we can make use of in heat exchangers,central heating
systems and in the provision of lighting systems and numerous electrical goods used in buildings. We
therefore need to gain an insight into the properties of metals and the reasons for them.We shall ﬁnd that
all these properties arise from the highly ordered, crystalline structures found in metals and alloys.
In the previous chapter we have examined the nature of atomic bonding, and we have seen how metals
as a class have very ordered, crystal structures. In the next chapter we shall examine in more detail
the mechanical properties of materials, and it is the task of this chapter to examine in simple terms
how the mechanical and physical properties of metals,including those mentioned above,are a consequence
of their crystalline nature.
3.2 Crystalline structure of metals
Metals are crystalline, that is to say their atoms are arranged in patterns with the highest degree of
symmetry and order of any of the materials used by man.Their properties, including their strength and
ductility, their excellent thermal and electrical conductivities all arise from their crystallinity. We shall
therefore examine the crystal structures of the metals commonly used in construction. The bonding
between the atoms that make up metal crystals is also special, and is known as the metallic bond.We have
examined the various types of bonds between atoms in Chapter 2,and we have seen that chemical bonding
involves the extra-nuclear structure of atoms,i.e.the electronic structure.The atomic nucleus in all elements

Dislocations, imperfections, plastic flow
31
is orbited by electrons, the number of electrons depending on which element it is, i.e. what the atomic
number of the element is. It is the various kinds of interactions between these electrons that enable atoms
to bond together in different ways (ionic, covalent, metallic, etc.).
3.2.1 Crystal structures of the common metals
There are 14 types of crystal possible, with a crystalline atomic arrangement, but fortunately the metals of
common interest conform to three of the simplest of these, and we shall confine our attention to these
three arrangements. In Section 2.4 we saw that these three arrangements are:
body-centred cubic (BCC)
% face-centred cubic (FCC)
% hexagonal close-packed (HCP).
These atomic arrangements are shown again in Figure 3.1.
These crystal structures or atomic arrays are called crystal lattices by metallurgists and material scientists.
Are there any differences between these three crystal types? Does the structure have a noticeable effect on
the behaviour of the metal? The answer to these questions is yes, the structure does have an effect. Later
in this chapter we shall examine the processes of plastic or permanent deformation in metals, and we shall
see that deformation is accomplished by the movement of crystal defects called ‘dislocations’. Dislocation
movements are studied by crystallographers,and they have found that dislocations move by a process called
slip on close-packed planes of atoms along close-packed directions.We shall not discuss this in detail here,
but the crystal arrangement that has the most slip planes is the FCC structure.This being so, we would
expect that metals possessing an FCC structure to be the most ductile, i.e. capable of the most plastic
deformation before they fail.This is exactly what we find – the FCC metals are the most ductile.Aluminium,
copper, lead, silver and gold are all very ductile metals and they all have the FCC-type structure.
The other two types are less ductile; in general, BCC metals are less ductile than the FCC type, and
HCP metals possess lower ductility than the previous two. It is important to remember that all metals are
ductile; FCC metals are outstandingly ductile, with the other two being less so.
Compared with the other materials of construction, these metal crystal structures are the simplest. For
this reason, the metals were the first class of materials to have their structures investigated and to be well-
understood in work that was mainly conducted before the Second World War.The techniques that were
(a) BCC (b) FCC (c) HCP
Figure 3.1 (a) the body-centred cubic, (b) face-centred cubic and (c) hexagonal close-packed
arrangements of atoms
(After Callister, 1994)

32
Basic principles
used to investigate them, such as X-ray diffraction, were then used with others to elucidate the structures
of the other classes of materials in research carried out since the Second World War.As we shall see, the
properties of metals such as their excellent thermal and electrical conductivities,their ductility and fracture
behaviour derive from their crystalline nature.
We may ask why the atoms arrange themselves in this way, and the detailed answer to this question lies
in the ﬁeld of solid state physics. However, the simple answer is that there are forces of both attraction and
repulsion acting between the atoms.With a lattice at room temperature, the distance between the atoms is
always the same.This is true for any piece of iron anywhere on planet Earth.The distance between the
atoms in a piece of gold will be different, but again, constant for any other piece of gold, and so on.This
inter-atomic spacing is sometimes called the lattice parameter, and values for all metals can be found in
textbooks on crystallography.The lattice parameters for a few common metals are given in Table 3.1.
These inter-atomic spacing vales are constant because of the balance of forces existing between the
atoms composing the crystals.We shall examine the nature and balance of these inter-atomic forces in
the next section.
3.2.2 Forces between atoms in crystals
The atoms separate themselves at a distance at which the forces of attraction and repulsion between the
atoms are equal.The inter-atomic spacings given above are the same for a piece of copper or iron wherever
in the world they are produced.Figure 3.2 shows the relationship between the separating distance between
two atoms in a crystal and the force existing between them.
The line shown in Figure 3.2 shows the resultant force acting between the atoms as a function of the
separation distance between them. This line is the resultant of two other graphs; the graph showing
the attractive force between atoms as a function of separation distance, and another showing the repulsive
force as a function of separating distance.We can see that if we put the lattice into tension,we get a positive
tensile resisting force, and if we compress the lattice we experience a negative compressive force of
resistance. Note also that the graph has a virtually linear slope in the region of the neutral or strain-free
position.This explains Hooke’s Law: the load is proportional to extension in an elastic solid, i.e. the stress
vs strain graph is linear in the elastic region.
If we heat the metal, its atoms will gain energy, and the repulsive forces will increase slightly, and this
will result in the inter-atomic spacing increasing slightly, giving rise to the familiar thermal expansion
effects observed in metals when they are heated. We shall look at this again in Chapter 6. Let us now
consider the mechanical (stress–strain) properties of metals.
Table 3.1 Inter-atomic distances, atomic radii and crystal type for some common metals
Metal Crystal structure type Inter-atomic distance (nm) Atomic radius (nm)
Aluminium FCC 0.2862 0.1431
Copper FCC 0.2556 0.1278
Iron (a) BCC 0.24824 0.12412
Iron (c) FCC 0.2540 0.1270
Nickel FCC 0.2491 0.1246
Zinc HCP 0.2665 0.1390
Lead FCC 0.3499 0.1750
Magnesium HCP 0.3209 0.1610
Silver FCC 0.2888 0.1444
Gold FCC 0.2882 0.1441

33
Interatomic force
(tension)
This part is
nearly straight Interatomic distance
(tension)
Interatomic
distance
(compression)
Interatomic force
(compression)
Neutral or strain-free position
Figure 3.2 Relationship between the distance between two atoms and the force between them
(After Gordon, 1971)
3.3 Stress vs strain behaviour of metals
Metals, and particularly steel, are of vital importance in construction and civil engineering; indeed, the
construction of most of the impressive buildings,bridges and other structures created during the twentieth
century would not have been possible without steel.For this reason it will be very worthwhile to examine
the load-bearing behaviour of steel.
The stress vs strain graph obtained by testing a metal such as plain carbon steel to destruction is
shown in Figure 3.3. We can immediately see that the line consists of two regions; an initial linear
portion, followed by a non-linear portion. The last point on the curve, marked by a small cross, is the
point of fracture, i.e. this is the point at which the test piece can sustain no more strain and it fails.
In this case, we can see that failure has occurred at a strain of 42.5 per cent. This means that the test
piece gauge length was 42.5 per cent longer than it was at the start of the test. Furthermore, this
42.5 per cent extension was permanent extension.The 42.5 per cent was measured by putting the broken
test piece ends together in an extensometer gauge and measuring the new length as at the point of
fracture.
What happened to the steel as it was strained from zero to the point of fracture? What processes
occurred inside the metal that resulted in the stress–strain graph being of the form that we observe? To
answer these questions, we need to take a look at the structure of metals, i.e. at how the atoms of which
they are composed are arranged.

34
Basic principles
3.3.1 Crystal structure of steel
Steel is iron with a small amount of carbon added to it.The addition is typically less than 1.0 per cent;
many structural steels contain about 0.4 per cent carbon. So steel consists of iron crystals, with a
small amount of iron carbide (Fe3
C) present in the microstructure.We need not consider the metallurgy
of steel in any depth here. At room temperature iron crystals have the BCC-type structure, as shown in
Figure 3.4.
3.3.2 Elastic behaviour
The spacing between the atoms is the separation at which the force of attraction is exactly balanced by
the force of repulsion. This is logical, and it is the basis of elastic behaviour in metals. The result of these
forces of attraction and repulsion is that they resist any applied loading, and as a result, we can
model a metal crystal as a lattice where the atoms are attached to each other by springs, as shown in
Figure 3.5.
This spring model can help us understand the elasticity of metals. By elastic deformation we mean
temporary and recoverable deformation.We stretch a piece of rubber or a spring and it extends.When we
release one end of the rubber or spring, it immediately ‘springs back’ to the original length it had before
we stretched it.We see exactly the same behaviour in compression or torsion. Load, deform followed by
400
300
200
100
0
0 10 20 30 40
STRAIN %
STRESS
N/mm2
Figure 3.3 Stress vs strain graph for a 0.1 per cent carbon steel

35
Figure 3.4 The arrangement of atoms in the BCC structure
Figure 3.5 Material in the unstrained condition
spring-back when the load is released. This behaviour is illustrated in Figure 3.6. This shows both the
tensile and compressive loading situations.
If we apply a tensile load to our metal, we stretch it, and it resists our stretching – we can feel the
resistance.What is happening, and where does the resisting force come from? Remember, we are looking
at elastic behaviour.
When we apply a tensile load to our metal, at the crystal level it is like pulling the atoms apart.
Our tensile load is resisted by the forces of attraction between the atoms, at the same time our force
acts with the forces of repulsion between the atoms.Therefore the atoms move apart until the applied
force is balanced once more by the forces of attraction. If we release our force, the attractive forces
pull the atoms back to the original point of balance, and our temporary elastic extension goes back
to zero. The same thing happens in reverse if we apply a compressive load. In this case we work with
the forces of attraction and against the forces of repulsion, and so we get a temporary elastic com-
pression.When we release our applied load, the forces of repulsion push the atoms back to their original
spacing.

36
Basic principles
3.3.3 The elastic modulus or stiffness – a fundamental property
When we apply any load to any structure, it will deflect elastically. Even the weight of a couple of seagulls
standing on a battleship gun-barrel will cause it to deflect elastically. In this case the deflection will be too
small to measure with any extensometer or normal strain measurement device, but deflection will occur
nevertheless.Finally,note that with elastic deformation the atoms stay in the same relative positions to each
other; i.e. no atom shifts its position relative to its neighbours.
In construction,we require materials with a high stiffness for the structural or load-bearing elements of
our buildings. By high stiffness we mean capable of load bearing with relatively small elastic deformation.
For example, the Empire State Building in New York weighs something over 300,000 tonnes, and this
enormous weight has to be carried by the structural frame of the building at ground level.As we move up
the building, the load that has to be carried by the structure at that level decreases, of course. However,
300,000 tonnes is a very high load, and it is important that the material of the frame is both strong
in compression and also of high stiffness. In fact, the Empire State Building is about 165 mm shorter
than it should be in the unloaded condition, purely because of its high weight. The action of
300,000 tonnes acting in compression has shortened the building elastically by 165 mm. The frame
of the Empire State Building is made from steel, which is both strong in compression and also of
high stiffness.
The value of Young’s modulus depends upon the strength of the bonds between the atoms in the
crystal. This bond strength also plays an important part in determining how strong the metal is, and
(a) (b)
Figure 3.6 (a) Material strained in tension, atoms pulled further apart, material elongates; (b) material
strained in compression, atoms pushed closer together, material becomes shorter

37
Unit area, crossed by
r
r0
σ
r0
r0
bonds
I
r2
0
Figure 3.7 Showing the elastic straining of bonds in a material put into tension
(After Ashby Jones, 1980)
Table 3.2 Values of strength, stiffness and melting temperature for a range of elements
Element Yield strength (MPa) Stiffness (E) (GPa) Melting/softening temperature °C
Diamond 50,000 1,000 3,800
Tungsten 6,000 450–650 3,380
Steel, 0.4% C 400 200 1,450
Iron 50 196 1,537
Copper 60 124 1,083
Aluminium 40 69 660
Lead 11 14 327
since melting also involves breaking bonds, it will play a part in determining the melting temp-
erature as well. Therefore we ﬁnd that, as a general rule, elements having high strength and hardness
also have high values of elastic modulus, E, and melting temperature. The data given in Table 3.2
illustrate this.
The data in Table 3.2 illustrate that diamond, which has the strongest bonding between its atoms, has
the highest values of strength,stiffness and melting/softening temperature.Lead,with the weakest bonding
of the materials shown, has the lowest values in each case.
To gain an idea of what is involved in elastic deformation, imagine a piece of material being loaded in
tension. Looking at Figure 3.7, we can see that the load is carried by all the bonds in the cross-section of
the material.The result, as we know, will be a slight increase in the length of the piece of material. If we
release the tension, the piece of material will immediately spring back to its original length.This is elastic
behaviour. Elastic strains are temporary, and are relaxed as soon as loading is removed.The same thing will
be observed if we apply a compressive load.
Having examined elastic behaviour, now let us look at plastic behaviour.

38
Basic principles
3.3.4 Plastic behaviour
This is sometimes referred to as inelastic behaviour to distinguish it from elasticity. Plastic strains are
permanent strains. There is no ‘spring back’. Since there is a permanent shape change when plastic
deformation occurs, there must be some relative movement of the atoms in the crystals. Furthermore,
this movement must be able to occur without fracturing of the crystals.What mechanism allows this to
happen?
In Figure 3.3, we saw that the initial portion of the graph was a straight line; this is the elastic part
of the stress–strain behaviour.Within this region, if we double the load or stress, we double the extension
or strain.This is known as Hook’s Law, as it was first enunciated by Robert Hooke in the seventeenth
century. Elastic behaviour is sometimes called linear behaviour because it is described mathematically by a
straight line. However, the straight line reaches a peak, and then (in the case of steel) it falls, and thereafter
the line is non-linear.This non-linear behaviour is called plastic deformation.The elastic or straight line
behaviour is a fundamental property of the metal, and Young’s modulus is a constant for the particular
metal.The plastic behaviour is not fundamental,and the shape of the plastic flow curve can vary depending
upon how fast we deform the metal, or upon the state of stress in the metal, or upon the temperature
of the metal. Furthermore, the end of the plastic flow curve is the process of fracture, when the metal
reaches the limit of its capacity to deform further, and it fails.What mechanism is required to accomplish
this? The answer lies in a type of crystal defect called dislocations, and we shall examine these next.
3.4 Defects in crystals
The structure of a perfect crystal with a cubic lattice is shown in Figure 3.8.We can see that every atom is
at a cube corner, i.e. they all occupy the correct places on the crystal lattice.
However,this situation will obtain at a temperature of absolute zero,but not at normal room temperature.
In reality, metal crystals will contain crystal defects of various kinds, including vacancies, interstitialcies,
Figure 3.8 The structure of a perfect cubic crystal lattice

39
Figure 3.9 A dislocation in a cubic crystal
stacking faults and dislocations. We shall mainly consider dislocations here, as the others play a lesser
role in plastic behaviour.What is a dislocation? A simple cubic crystal containing a dislocation is shown in
Figure 3.9.
How does the dislocation make possible plastic deformation without failure?To answer this we need to
consider what happens if a shear force is applied to a crystal containing a dislocation.
3.4.1 Crystal imperfections
The arrangements of atoms shown in Figure 3.8 in the last section are ideal or perfect arrangements.They
would be seen as described at absolute zero, i.e. a temperature of –273 °C. However, at normal room
temperature of, say, 20 °C, the crystals will not be perfect, but will contain imperfections or defects of
various kinds: point, line and area defects.
% Point defects include:
– vacancies: a vacancy is a site on a lattice not occupied by an atom;
– solute atoms: this is a site on a lattice occupied by an atom of a different species;
– interstitials: these are atoms forced into the spaces between other atoms on the lattice.
% Line defects: dislocations are easily the most important of this type.
% Area defects: stacking faults are examples of this type.
From the point of view of construction materials, easily the most important type of defect is the edge
dislocation. This is because an understanding of the dislocation enables us to understand the plastic
deformation and fracture of engineering materials.Figure 3.10 shows the various types of point defect that
can exist in a metal crystal.

40
Basic principles
Self-interstitial Interstitial atom
Sutstitutional
atom
Vacancy
Figure 3.10 The various types of point defect that can exist in a metal crystal
(After Anderson et al., 1974)
3.4.2 Dislocations and plastic flow
Figure 3.9 shows a crystal containing a single edge dislocation, and the presence of such dislocations in
metals was first proposed in 1934 to explain their plastic properties, although at that time there was no
direct evidence for their existence. Experimental evidence for the actual existence of dislocations had to
wait for 20 years; however, they are now very well understood. The movement of dislocations is the
mechanism, at the microscopic level, by which the metal can be given a permanent change of shape. So
when a metal is rolled into sheet or strip, or forged, the rolls or the forging dies are causing millions upon
millions of dislocations to move within the crystals of which the metal is composed.
Figure 3.11 shows how the application of shear forces can cause a dislocation to move along a slip plane,
resulting in the permanent movement of the block of atoms above the slip plane by one inter-atomic
spacing relative to the lower block of atoms. Cleavage and fracture of the metal crystal does not occur.The
passage of ten dislocations will result in shear movement of ten inter-atomic distances, and so on. Since
hundreds of millions of dislocations will be moved in each crystal, when they are deformed we can easily
see how measurable plastic strains are produced.
The dislocation density increases as a metal is cold worked.The number of dislocations in unit volume
of crystal, dislocation density N, is defined as the total length of dislocations l per unit volume, N = l / V,
normally quoted in units of cm–2
.For a well-annealed metal crystal,N is usually between 106
and 108
cm–2
,
but it can be as low as 102
cm–2
with very careful preparation. For a heavily cold-rolled metal N can be
around 5 # 1011
cm–2
(Hull, 1968).
3.4.3 Plastic deformation of metals
Plastic deformation is permanent deformation, as distinct from elastic deformation, which is temp-
orary. We now know what a dislocation is, so we shall next examine what happens when a

41
Slip
Plane
(a)
3 2
4 5
1 3
(c)
3 2
4 5
1
(b)
4
2 1
5
τ
τ (d)
3
b
2 1
τ
τ
4 5
Figure 3.11 How a dislocation enables slip to occur in a metal crystal without cleavage fracture
occurring
(After Anderson et al., 1974)
dislocation moves. We shall look at what happens when the dislocation moves by one inter-atomic
spacing.
Deformation occurs essentially by a shearing process, i.e. a process where one plane of atoms slides
or glides over the underlying layer. However, if the plane were to glide all at once, this would imply that
all the bonds between the two planes of atoms would need to be broken at once. If this happened, the
metal crystal would split and cleave into two halves.That this does not occur is proved by the excellent
ductility that most pure metals and alloys normally exhibit. The exact way in which this shearing was
accomplished puzzled metallurgists at first, until in 1934 three people independently published papers
describing how it could happen.At the time they had no direct physical evidence for the existence of the
crystal dislocations described above. They had to postulate their existence in metal crystals, and their
predictions were eventually proved to be correct over 20 years later following the development of powerful
electron microscopes.
3.4.4 Effects of temperature on plastic flow
One of the earliest references to the working of metals is found in the Bible, in the Book of
Genesis. It refers to oneTubal Cain, a skilled worker of metals. From the earliest times, smiths have known
that metals can be shaped by forging when they are hot. In the case of steel, this means when they are
heated to at least red heat.When cold, metals are much harder and stronger, and more difficult to forge.
Why is this?

42
Basic principles
Again, it is explicable in terms of the defect population, and in particular, the numbers of dislocations
present in the crystals of which they are composed.The number of dislocations present in a metal crystal
is strongly inﬂuenced by temperature. At absolute zero (–273 °C), metal crystals may be thought of as
perfect for all intents and purposes. As they are heated up from absolute zero, dislocations appear in the
microstructure.As heating continues, the multiplication of dislocations continues. So the structure of hot
metal is said to be more disordered than that of cold metal. Dislocation multiplication continues until the
metal reaches its melting temperature, when there is a state change from solid to liquid.
However, the multiplication of dislocations does not increase linearly with temperature, but
rather follows an Arrhenius or exponential relationship.The number of dislocations N is proportional to
exp – (Q / RT), where Q is an activation energy, R is the gas constant and T is the temperature. Because
the index is negative, an increase in temperature produces a rapid non-linear increase in N.
3.4.5 Polycrystalline aggregates
In real metals as we encounter them in the construction industry, they do not consist of single crystals, but
rather of polycrystalline aggregates.That is to say,a piece of steel will not consist of a single iron crystal but
of thousands of iron crystals all joined together at their grain boundaries.
Each grain in Figure 3.12 represents a single crystal, i.e. the atomic arrangement in each grain is a
regular crystal.The planes of atoms in the grain next door will also be regular, but will not be parallel to
the planes of atoms in its neighbouring crystals. So each grain represents a very ordered structure, and the
grain boundaries are relatively disordered. Such a structure is called a polycrystalline aggregate, because it is
made up of many crystals.A steel I-beam in a building structure will be made up of billions of iron crystals
containing typically 0.3–0.4 per cent carbon.Nearly all metallic engineering components are polycrystalline.
Very occasionally, we deliberately make components out of a single crystal, one example being a turbine
blade for the high-temperature portion of an aircraft engine.
Figure 3.12 The microstructure of a pure metal, showing the grain (crystal) boundary arrangement
(After Tylecote, 1992)

43
3.4.6 Importance of ductility in structural steel
We know that for construction purposes, structural steels are often selected with a carbon content
of 0.4 per cent, a composition offering a good combination of strength and ductility. The ductility is
important, for reasons of safety. We can never predict every loading situation on a building during its
design life, but the over-riding consideration is always life safety.While we can predict wind speeds and
loadings,and all the likely effects of normal day-to-day operation of the building,there are possibilities that
are not foreseeable.The impact of the B25 bomber that struck the Empire State Building in NewYork in
July 1945 was not predictable, it was an accident. Since those days we have become familiar with
urban terrorism, and the planting of bombs and their effects on buildings. The attack on the World
Trade Center in New York in September 2001 was also an aircraft impact, and it was not accidental,
but deliberately done.
While we cannot foresee these events, we still need to make our buildings as safe as possible. Iconic
buildings of the past, such as the great Pharos Lighthouse in Alexandria in Egypt, or the great tomb of
Mausolus at Harlicarnassus were two of the Wonders of the Ancient World, and lasted for many centuries.
They were both destroyed by earthquakes in the thirteenth century, and so did not survive for us to see
them.The reason they did not survive the earthquakes was that they were made of brittle materials.
When a brittle material is loaded, it deforms elastically until it reaches its elastic limit. However,
when its capacity for elastic distortion is reached, it just fractures without warning. So if a building is
made of natural stone, which is brittle, the kind of violent dynamic loading experienced during an
earthquake would be likely to cause the stone to be loaded to its elastic limit. Portions of the structure
loaded to the limit would then fail by brittle fracture, resulting in collapse of the whole edifice.This was
the fate of the Pharos Lighthouse and King Mausolus’ tomb. It is thought that the Pharos Lighthouse was
perhaps close to 100 metres in height, and it was this great height that made it an ancient wonder. In our
modern age we routinely construct buildings three or four times as high.This has been made possible by
the availability of steel in large quantities and at low cost. Buildings this high have either a steel frame or a
steel-reinforced concrete frame.
3.4.7 Strengthening mechanisms in metals
Since deforming metals plastically involves moving dislocations,anything that makes dislocations harder to
move will have the effect of hardening and strengthening a metal. Now that we know about dislocation
glide, we can appreciate that any impediment to the glide process, which either prevents it from occurring
or which makes it more difficult, will cause the metal to become harder and stronger. By harder and
stronger, we imply that the metal becomes more resistant to permanent deformation.
The things that will make dislocation movement more difficult include the presence of solute atoms in
the crystal lattice,the presence of grain boundaries,because dislocation movement must stop when the line
reaches the edge of the crystal and the effects of cold work. Let us examine, in simple terms, how these
strengthening mechanisms work.
Solute hardening works because solute atoms will not be the same size as those of the parent lattice.
They will therefore have a distorting effect on the parent lattice.To accommodate the larger (or smaller)
diameter atom the lattice will be deformed in the zone around the solute atom.Therefore the crystal planes
on which slip might occur are curved or bent instead of being straight,and this makes slip along that plane
more difficult.
Grain boundaries represent areas of relative disorder, and since they also represent the place where the
slip plane terminates, slip will stop at the grain boundary.This is shown in Figure 3.13.
The other phenomenon that will make slip more difficult is the presence of cold work. As plastic
deformation occurs, the density of dislocations increases, and the crystals become distorted. Those

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distinguished parliament men and persons of standing at the Court.
At last the king, whose portrait he afterwards engraved in different
sizes—as often as eleven times—gave him a number of sittings, after
which Nanteuil received a pension and the title of Dessinateur du
Cabinet.36
Louis XIV. was not satisfied with thus rewarding a talent already
recognised as superior; he was also desirous of stimulating by
general measures the development of what he had himself declared
a liberal art.37 Engravers were privileged to exercise it without
being subjected to any apprenticeship, or controlled by other laws
than those of their own genius; and seven years later (1667) the
royal establishment at the Gobelins became virtually a school of
engraving. Whilst Lebrun, its first director-in-chief, assembled therein
an army of painters, draughtsmen, and even sculptors, and wrought
from his own designs the tapestries of the Éléments and the
Saisons, Sebastien Leclerc superintended the labours of a large
body of native and foreign engravers, entertained at the king's
expense.
One of these, Edelinck, had been summoned to France by
Colbert. Born at Antwerp in 1640, and a contemporary of the
engravers trained by the disciples of Rubens himself, he was
distinguished, like them, by his vigour of handling and knowledge of
effect. Once settled in Paris, he supplemented these Flemish
characteristics with qualities distinctively French, and was soon a
foremost engraver of his time. Endowed with singular insight and
elasticity of mind, he readily assimilated, and sometimes even
improved upon, the style of those painters whom he reproduced,
and adopted a new sentiment with every new original. He began, in
France, with an engraving of Raphael's Holy Family, the so-called
Vierge de François I., which is severe in aspect, and altogether
Italian in drawing; and he followed this up with plates of the
Madeleine of Lebrun, his Christ aux Anges, and his Famille de
Darius, all of them admirable reproductions, in which the defects of
the originals are modified, while their beauties are increased by the
use of methods which make their peculiar and essential

characteristics none the less conspicuous. In interpreting Lebrun,
Edelinck altered neither his significance nor his style; he only
touched his work with fresh truth and nature: as, when dealing with
Rigaud, he converted that artist's pomposity and flourish into a
certain opulence and vigour. When, on the contrary, he had to
interpret a work stamped with calm and reflective genius, his own
bold and brilliant talent became impregnated with serenity, and he
could execute with a marvellous reticence such a translation as that
from Philippe de Champagne—the painter's portrait of himself—a
favourite, it is said with the engraver, and one of the masterpieces of
the art.
When Edelinck arrived in Paris, Nanteuil, his senior by some
fifteen years, had a studio at the Gobelins, close to the one where
he himself was installed. This seeming equality in the favour
accorded to two men, then so unequal in reputation and
achievement, would be astonishing unless we remember the object
which brought them together, and the very spirit of the institution.
Things went on in the Gobelins almost as they did in Florence, in
the gardens of San Marco, under Lorenzo de' Medici. Artists of
repute worked side by side with beginners: not indeed together, but
near enough for the master continually to help the student, and for
the spirit of rivalry, the excitement of example, to keep alive a
universal continuity of effort. French art had been lately honoured by
three painters of the highest order—Poussin, Claude38 and Lesueur;
but the first two lived in retirement, and far from France; whilst the
third had died leaving no pupils, and, consequently, no tradition. It
seemed urgent, therefore, in order to perpetuate the glory of the
school, to gather together both men of mature talent and men
whose talent was yet young and unformed, and to impel them all
towards a common object on a common line of work. Colbert it was
who conceived and executed the plan, who assembled all the great
masters in painting, sculpture, and engraving, whose services he
could command, without omitting any younger men who might seem
worthy of encouragement. He quartered them all at the Gobelins,
and put over them the man best fitted to play the part of their

organiser and supreme director. There was a pre-established
harmony between Louis XIV. and Lebrun, says M. Vitet39 and when
the painter died (1690), neither he nor his master had as yet
permitted any encroachment upon their territory. Lebrun might
have appropriated a famous saying of the king, applied it to his own
absolute supremacy, and said, with truth, that he alone was French
art. Everything connected with the art of design, whether directly or
indirectly, from statues and pictures for public buildings down to
furniture and gold plate, were all subject to his authority, and were
all moulded by his influence. It was an unfortunate influence in some
respects, for it made the painting and sculpture of the epoch
monotonously bombastic; but to engraving, under whose auspices
contemporary pictures were sometimes transformed into real
masterpieces, it cannot be said to have been unfavourable.
Fig. 83.—JEAN PESNE.
The Entombment. After Poussin.

When Lebrun was called to the government of the arts, the
number of practical engravers in France was already considerable.
Jean Pesne, the special interpreter of Poussin, had published several
of those vigorous prints which even now shed honour on the name
of the engraver of the Évanouissement d'Esther, of the Testament
d'Eudamidas, and of the Sept Sacrements. Claudine Bouzonnet,
surnamed Claudia Stella, who by the force of her extraordinary gift
has won her way to the highest rank among female engravers,
Étienne Baudet, and Gantrel—all these, like Jean Pesne, applied
themselves almost exclusively to the task of reproducing the
compositions of the noble painter of Les Andelys. On the other hand,
François de Poilly, Roullet, and Masson (the last so celebrated for his
portrait of Count d'Harcourt, and his Pilgrims of Emmaus, after
Titian), and many others equally well known, had won their spurs
before they devoted themselves to the reproduction of Lebrun.
Finally, Nanteuil, who only engraved a few portraits from originals by
the director, was already widely known when Colbert requested him
to join, among the first, the brotherhood which he had founded at
the Gobelins. As soon as in his turn Edelinck was admitted, he
hastened to profit by the advice of the master whom it was his
privilege to be associated with; and, aided by Nanteuil's example,
and under Nanteuil's eye, he soon tried his hand in the production of
engraved portraits.
No one indeed could be better fitted than Nanteuil to teach this
special art, in which he has had few rivals and no superior. Even
now, when we consider these admirable portraits of his, we are as
certain of the likeness as if we had known the sitters. Everybody's
expression is so clearly defined, the character of his physiognomy so
accurately portrayed, that it is impossible to doubt the absolute truth
of the representation. There is no touch of picturesque affectation in
the details; no exaggerated nicety of means; no trick, nor
mannerism of any sort; but always clear and limpid workmanship,
and style so reticent, so measured, that at first glance there is a
certain indescribable appearance of coldness, no hindrance to
persons of taste, but a pitfall to such eager and hasty judgments as,

to be conquered, must be carried by storm. Nanteuil's portraits come
before us in all the outward calm of nature; possibly they seem
almost inartistic because they make no parade of artifice; but, once
examined with attention, they discover that highest and rarest form
of merit which is concealed under an appearance of simplicity.
If the Turenne, the Président de Bellièvre, the Van
Steenberghen (called the Avocat de Hollande), the Pierre de
Maridat, the Lamothe Le Vayer, the Loret, and others, are
masterpieces of refinement in expression and drawing, they also
prove, as regards execution, the exquisite taste and the marvellous
dexterity of the engraver. But to discern the variety of method they
display, and to perceive that the handling is as sure and fertile as it
is learned and unpretentious, they must be closely studied.
As a rule, Nanteuil employs in his half-lights dots arranged at
varying distances, according to the force of colouring required, in
combination with short strokes of exceeding fineness. Sometimes—
as, for instance, in the Christine de Suède, altogether engraved in
this manner—the process suffices him not only to model such parts
as verge upon his lights, but even to construct the masses of his
shadows. The Edouard Molé is, on the contrary, in pure line. The
soft silkiness of hair he often expresses by free and flowing lines,
some of which, breaking away from the principal mass, are relieved
against the background, breaking the monotony of the
workmanship, and suggesting movement by their vagueness of
contour. Often, too, certain loose lines, either broken or continued
without crossing in different directions, admirably distinguish the
natures of certain substances, and imitate to perfection the soft
richness of furs or the sheen of satin. Yet it sometimes happens that
in the master's hand the same method results in the most opposite
effects: a print, for instance, may exemplify in its treatment of the
textures of flesh a method applied elsewhere, and with equal
success, to the rendering of draperies. In a word, Nanteuil does not
appropriate any particular process to any predetermined purpose.
While judiciously subordinating each to propriety, he can, when he

pleases, make the most of all; and whatever path he follows, it
always appears that he has taken the best to reach his end.
It was not only to the teaching of Nanteuil that Edelinck had
recourse; he still further improved his style by studying his
countryman, Nicolas Pitau (whom Colbert had also summoned from
Antwerp to the Gobelins), and afterwards by acquiring the secret of
brilliant handling from François de Poilly. To which of these engravers
he was most indebted is a point which cannot be exactly
determined. After investing himself with qualities from each, he did
not imitate one more than another; he found his inspiration in the
examples of all three.
Nanteuil and Edelinck, first united by their work, were soon fast
friends, in spite of the difference of their ages, and the still greater
difference of their tastes. The French engraver sent for his wife from
Rheims as soon as he found himself in a fair way to success and
fortune; but he had also in some degree returned to the habits of his
youth. A shining light in society, and as intimate with the cultured
set at Mlle. de Scudéry's as with the devotees of pleasures less
strictly intellectual, his career of dissipation in the salons and
fashionable taverns of the day contrasts strangely with the sober
quality of his talent, and increases our surprise at the number of
works which he produced. Even his declining health did not change
his habits. Till the end he continued to divide his time between his
work and the world; and at his death, in 1678, at the age of fifty-
two, he left nothing, or almost nothing, to his wife, in spite of the
large sums he had made since he came to Paris.

Fig. 84.—JEAN PESNE.
Nicolas Poussin.
Edelinck's fate was very different. He lived in seclusion, given
over to his art and to the one ambition of becoming churchwarden
(marguillier) of his parish: a position refused him, it is said, as
reserved for tradesmen and official personages, and with which he
was only at length invested by the condescending interference of the
king. It was probably the only favour personally solicited by Edelinck,
but it was by no means the first he owed to the protection of Louis
XIV. Before the churchwardenship he held the title of Premier
Dessinateur du Cabinet. Like Lebrun, like Mansart and Le Nôtre, he
was a Knight of St. Michael and the Academy of Painting elected him

as one of its council. His old age, like the rest of his days, was quiet
and laborious; and when he died (1707) his two brothers and his
son Nicolas, who had all three been his pupils, inherited a fortune as
wisely husbanded as it had been honourably acquired.
Edelinck survived the principal engravers of the reign of Louis
XIV. François de Poilly, Roullet, Masson, and Jean Pesne, had more
or less closely followed Nanteuil to the grave. At the Gobelins, once
so rich in ability of the first order, students had taken the place of
masters, and clever craftsmen succeeded to artists of genuine
inspiration. Van Schuppen had followed Nanteuil, as Mignard had
Lebrun, from necessity rather than right. And last of all, Gérard
Audran, the most distinguished engraver of the time—whom, for the
sake of clearness in our narrative, we have not yet mentioned—had
died in 1703; and though members of his family did honour to the
name he had distinguished, none of them were able to sustain the
full weight of its glory.

Fig. 85.—GÉRARD AUDRAN.
La Noblesse. After Raphael.
One would hardly venture to say that Gérard Audran was an
engraver of genius, because it does not seem permissible to apply
the term to one whose business it is to interpret the creations of
others, and subordinate himself to models he has not himself
designed; yet how else can one characterise a talent so full of life,
so startling a capacity for feeling, and a method at once so large, so
unstudied, and so original? Do not the plates of Gérard Audran bear
witness to something more than mere superficial skill? Do they not
rather reveal qualities more subtle—a something personal and living,

which raises them to the rank of imaginative work? Their real fault,
perhaps—at least the fault of those after Lebrun or Mignard—is that
they are not reproductions of a purer type of beauty. And even these
masters are so far dignified by the creative touch of their translator
as almost to seem worthy of unreserved admiration. We can
understand the mistake of the Italians, who thought, when they saw
the Batailles d'Alexandre, in black and white, that France, too, had
her Raphael, when, in reality, allowing for difference of manner, she
could only glory in another Marc Antonio.
Fig. 86.—GÉRARD AUDRAN.
Navigation. After Raphael.

Gérard Audran was born in Lyons in 1640, and there obtained
from his father his first lessons in art. Afterwards he went to Paris,
and placed himself under the most famous masters of the day, by
whose aid he was soon introduced to Lebrun, and at once
commissioned to engrave one of Raphael's compositions. When
Audran undertook the work, he had not the picture before him, as
Edelinck had when he engraved the Vierge de François I. His
original was only a pencil copy which Lebrun had brought back from
Italy; hence no doubt the modern character and the French style
which are stamped on the engraving. Feeling dissatisfied with his
work, the young artist did not publish it, but determined to study the
Italians in Italy, to educate himself directly from their works, and
thenceforth to engrave only those pictures of which he could judge
at first-hand without the danger of an intermediary. He set off
therefore for Rome, and remained there for three years, during
which time he produced several copies painted at the Vatican, many
drawings from the antique, several plates after Raphael,
Domenichino, and the Carraccis, and the engraving of a ceiling by
Pietro da Cortona, which last he dedicated to Colbert.
By this act of homage he acquitted himself of a debt of gratitude
to the minister who had favoured him ever since his arrival in Paris,
and who, at Lebrun's request, had supplied the means of his sojourn
in Italy. On Colbert's part it was only an act of justice to recall
Audran to France, and to entrust him with the engraving of the lately
finished series of the Batailles d'Alexandre, for the great
publication called the Cabinet du Roi. To the engraver, then
twenty-seven years old, a pension was granted, with a studio at the
Gobelins, then the customary reward of talents brilliantly displayed.
It may be added that six years (1672–1678) sufficed him to finish
the stupendous task.
Treated as a friend, and almost on an equal footing, by Lebrun,
who for no one else departed from the routine of his official
supremacy, Audran exerted over the king's chief painter a
considerable, if a secret, influence. In spite of all that has been
said40 Lebrun was not the kind of man to openly question his own

infallibility, nor to advertise his deference to the advice of an artist so
much younger than himself, his pupil, so to speak, and consequently
without the authority of any higher degree; yet he frequently
consulted him, and took his advice, in private. Also (and this is
significant) when the engravings of the Batailles appeared—
engravings to a certain extent unfaithful, inasmuch as they differed
decidedly from the originals—the fact that the painter made no
complaint points to his recognition in Audran of the right to correct,
and to his implicit submission to Audran's corrections.
In this respect Lebrun conducted himself as a man of the world,
and one well able to understand the true interests of his reputation.
He had everything to gain by giving full liberty to an engraver by
whose perfect taste the blunders of his own were corrected, and
who harmonised his frequently harsh and heavy colouring, and
strengthened in modelling and design his often undecided
expression of form. Thus the plates of the Batailles, in addition to
the high quality of the composition of the originals, present, alike in
general aspect and in detail, a decision which belongs to Audran
alone. Force and transparency of tone, largeness of effect, and,
above all, a distinctly marked feeling for characteristic truths, are
conspicuous in them. Not a single condition of art is imperfectly
fulfilled. Marc Antonio himself drew with no more certainty; the
Flemings themselves had no deeper knowledge of chiaroscuro; the
French engravers, not excepting even Edelinck41 have never treated
historical engraving with such ease and mäestria. In a word, none of
the most famous engravers of Europe have been, we believe, so
richly endowed with all artistic instincts, nor have better understood
their use.
The Batailles d'Alexandre finished, Audran engraved Lesueur's
Martyre de Saint Protais; several Poussins, amongst others the
Pyrrhus Sauvé, the Femme Adultère, and the radiant Triomphe
de la Vérité, one of the most beautiful (if not the most beautiful)
historical engravings ever published; and, after Mignard, the Peste
d'Égine, and the paintings in the cupola at Val-de-Grâce.

These several works, where elevation of taste and sentiment are
no less triumphantly manifest than in the Batailles themselves, are
also finished examples of engraving in the literal sense of the word.
Audran disdained to flaunt his skill, and to surprise the eye by
technical display, but he understood to the utmost all the secrets
and resources of the craft, and employed them with more ability
than any competitor. Associating engraving with etching, he
deepened with powerful touches of the burin those strokes of the
needle which had merely served to suggest outlines, masses of
shadow, and half-tints. On occasion, short strokes, free as a pencil's,
and seemingly drawn at random, with dots of different sizes,
distributed with apparent carelessness, sufficed for the modelling of
his forms; at others, he proceeded by a consistent system of cross-
hatching. Here rough etching work is tumbled about (so to speak) in
wild disorder; there a contrary effect is produced by nearly parallel
furrows scooped in the metal with methodical exactness; but
everywhere the choice and progress of the tools are based on
conditions inherent in the nature of the several objects, and their
relative positions and distances. Audran did not try to attract
attention to any of the methods he employed; he made each
heighten the effect of the other, and combined them all without
parade of ease, and yet without confusion.
So many admirable works secured for Audran a fame such as
Edelinck, as Nanteuil himself, had never obtained. The Academy of
Painting, which had welcomed him after the publication of his first
plates, elected him as one of its council in 1681. The school of
engraving which he opened grew larger than any other, and many of
his pupils became notable even in his company, and helped to
increase the renown of the master who had trained them.42
Towards the close of his life Audran laid by the burin for the pen.
Following Albert Dürer's example, he proposed to put together, in
the form of treatises, his life-long observations on the art he had so
successfully practised. Unfortunately, this task was interrupted by his
death; and, excepting a Recueil des Proportions du Corps Humain,
nothing is left us of those teachings which the greatest engraver, not

only of France, but perhaps of any school, had desired to hand on to
posterity.
By their works, Nanteuil, Audran, and the other masters of the
reign of Louis XIV., had popularised historical and portrait engraving
in France. The taste for prints spread more and more, and amateurs
began to make collections. At first they confined themselves to real
masterpieces; after which they began to covet the complete
achievement of peculiar engravers. The mania for rare prints became
fashionable; and we learn from La Bruyère that, before the end of
the century, some amateurs had already come to prefer engravings
presque pas tirées—engravings fitter to decorate the Petit-Pont or
the Rue Neuve on a holiday than to be hoarded in a collection—to
the most perfect specimens of the art. Others were chiefly occupied
with the bulk of their collections, and treasured up confused heaps
of all sorts of plates, good, bad, and indifferent. Others there were
who only cared about such as did not exceed a certain size; and it is
told of one devotee of this faith that, inasmuch as he would harbour
nothing in his portfolios but round engravings of exactly the same
circumference, he was used to cut ruthlessly to his pattern whatever
came into his hands. We must add that, side by side with such
maniacs, intelligent men like the Abbé de Marolles and the Marquis
de Béringhen increased their collections to good purpose, and were
content to bring together the most important specimens of ancient
engraving and such as best served to illustrate the more modern
progress of the art.
In France, however, it was not only the best expressions of
engraving that were considered. On the heels of the great engravers
there followed a crowd of second-rate workmen. Besides history and
portrait, every variety of print was published: domestic scenes,
architecture and topography, costumes, fêtes, and public
celebrations. The engraving of maps greatly improved under the
direction of Adrian and Guillaume Sanson, sons of the famous
Geographer in Ordinary to Louis XIII.

Jacques Gomboust, the king's Engineer in Ordinary for the
drawing up of plans of towns, published, as early as 1652, a map
of Paris and its suburbs in nine sheets, much more exact and more
carefully engraved than those of former reigns. Fashion plates were
multiplied ad infinitum; and a periodical called Le Mercure Galant
steadily produced new modes in apparel and personal ornaments.
Certain collections also, destined to perpetuate the remembrance of
the events of the reign, or the personal actions of the king, were
published by order, and at the expense of His Majesty, with a
luxury justified at any rate by the importance of the artists
participating in the work. The very almanacs bear the stamp of
talent, and are not unfrequently inscribed with the names of
celebrated engravers, such as Lepautre, François Spierre, Chauveau,
Sébastien Leclerc, and De Poilly.
In the days of Henri IV. and Louis XIII. almanacs were printed
on a single sheet, with a border sometimes of allegorical figures,
but, more often, composed simply of the attributes of the seasons.
It was under Louis XIV. that they at first appeared on larger paper,
and then in several sheets, wherein were represented the most
important events of the year, or, it might be, some ceremony or
court fête. In one is pictured the Battle of Senef, or the signing of
the Treaty of Nimeguen; in another, perhaps, the king is represented
dancing the Strasbourg minuet, or offering a collation to ladies. Of
course the majority of these prints are valueless in point of
execution, and are, moreover, of an almost purely commercial
character; but those which are poorest from an artistic point of view
are still worthy of interest, since they afford indisputable information
concerning the people and the habits and manners of the time.
Whilst many French artists were devoting themselves to the
engraving of subjects of manners or domestic scenes, or to the
illustration of books and almanacs, others were making satirical
sketches of current events and popular persons. The engraving of
caricatures, though it only dates from the middle of the seventeenth
century, had been practised long before in France and other
countries.

To say nothing of the Danses macabres, a sort of religious, or
at any rate philosophical, satire, we might mention certain
caricatures published even before the Carracci in Italy; in the Low
Countries in the time of Jerome Bosch and Breughel; in Germany in
the reign of Maximilian II.; and finally in France, in the reign of
Charles IX. But all these are either as stupidly licentious as those
afterwards made upon Henri III. and his courtiers, or as heavily
grotesque as those of the time of the League, towards the end of
the reign of Henri IV.
When Louis XIII. came to the throne, the wit of the caricaturists
was little keener, if we may judge by the coarse pictorial lazzi
inspired by the disgrace and death of the Maréchal d'Ancre, and the
Dutch and Spanish prints designed in ridicule of the French; but
some years later, when Callot had introduced into the treatment of
burlesque a keenness and delicacy which it could hardly have been
expected to attain, the comic prints assumed under the burin of
certain engravers an appearance of greater ingenuity and less
brutality.
It is needless to remark that at the beginning of the reign of
Louis XIV.—indeed, during the whole time of the Fronde and the
foreign occupation of a part of French territory—it was Mazarin and
the Spaniards who came in for all the epigrams. In the caricatures of
the day the Spaniards were invariably represented with enormous
ruffs, in tatters superbly worn, and, to complete the allusion to their
poverty, with bunches of beetroot and onions at their belts. There is
nothing particularly comic, nor especially refined, in the execution of
the prints. In piquancy and truth, these jokes about Spanish
manners and Spanish food recall those presently to be made in
England about Frenchmen, who are there invariably represented as
frog-eaters and dancing-masters. Yet comparing the facetiæ of that
period with the exaggerated or obscene humours which preceded
them, it seems as though the domain of caricature were even then
being opened up to worthy precursors of the lively draughtsmen of
the eighteenth and nineteenth centuries: in fact, as though some
Attic salt were already penetrating to Bœotia.

This advance is visible in the satires published towards the end
of the reign of Louis XIV. The Procession Monacale, a set of
twenty-four engravings which appeared in Holland (where many
Protestants had taken refuge), attacked with considerable vigour the
revocation of the Edict of Nantes, and the principal persons who had
participated in that measure. Louvois, Mme. de Maintenon, and all
the privy councillors of Louis XIV., are represented under the cowl,
and with significant attributes. Even the king figures in this series of
heroes of the New League; he is in a monk's frock like the others,
but a sun, in allusion to his lofty device, serves for his face, and this
hooded Phœbus bears in his hand a torch to light himself through
the surrounding darkness. The prints that make up this set, as well
as many more in the same style, are designed and engraved with a
certain amount of spirit. They serve to prove that in the frivolous
arts, as well as in the comic literature of the day, the object was to
make decent folk laugh, and to keep joking within bounds. In a
word, in comparison with former caricatures they are as the
vaudevilles of the Italian comedy to the farces once played on the
boards of strolling theatres.
Every sort of engraving being cultivated in France with more
success than anywhere else, under Louis XIV. the trade in prints
became one of the most flourishing branches of French industry. The
great historical plates, it is true—those at any rate which, like the
Batailles d'Alexandre, were published at the king's cost—were
chiefly sold in France, and were not often exported, save as presents
to sovereigns and ambassadors. But portraits, domestic scenes, and
fashion plates, were shipped off in thousands, and flooded all parts
of Europe. Before the second half of the seventeenth century, the
chief printsellers (for the most part engravers themselves and
publishers of their own works) were established in Paris on the Quai
de l'Horloge, or, like Abraham Bosse, in the interior of the Palace.
Rather later than this, the most popular shops were to be found in
the neighbourhood of the Church of St. Sèverin. If we examine the
prints then published in Paris, we may count as many as thirty
publishers living in the Rue St. Jacques alone, and amongst the

number are many famous names: as Gérard Audran, at the sign of
the Two Golden Pillars; François de Poilly, at the sign of St.
Benedict, and so forth.
Hence, we may mention, in passing, the mistake which
attributes to engravers of the greatest talent the production of bad
plates, to which they would never have put finger except to take
proofs. For instance, the words Gérard Audran excudit, to be found
at the bottom of many such, do not mean that they were engraved
by the master, but only published by him. Often, too, pseudonyms—
not always in the best possible taste—concealed the name of the
publisher and the place of publication: a precaution easily
understood, as it was generally applied to obscenities, and
particularly to those called pièces à surprise, which were then
becoming common, and continued to increase indefinitely during the
following century. True art, however, is but little concerned with such
curiosities; and it is best to look elsewhere for its manifestations.
The superior merit of the engraving of the masters of the French
school had attracted numbers of foreign artists to Paris. Many took
root there, amongst them Van Schuppen and the Flemings
commissioned to engrave the Victoires du Roi, painted by Van der
Meulen; others, having finished their course of study, returned to
their own countries, the missionaries of French doctrine and of
French manner. The result of this united influence was an almost
exact similarity in all the line engravings produced, by men of
whatever nationality or from whatever originals. Thus, the portraits
engraved by the German Johann Hainzelmann from Ulrich Mayer and
Joachim Sandrart, scarcely differ from those he had formerly
engraved from French artists: the Michel Le Tellier, for instance,
and the Président Dufour. The historical plates published about the
same time in Germany prove the same lively zeal in imitation. In
them art appears as, so to speak, a French subject; and Gustave
Ambling, Bartholomew Kilian43 and many more of their countrymen
—pupils, like these two, of François de Poilly—might be classed
amongst the engravers of the French school, if the style of their
work were the only thing to be considered.

An examination of the prints published by Flemish and Dutch
artists later than the school of Rubens and Van Dalen, would justify
a like observation. We may fairly regard Van Schuppen only as a
clever pupil of Nanteuil, and Cornelius Vermeulen as an imitator, less
successful, but no less subservient. And when we turn to the Italian
engravers of the seventeenth century, we find that, as a rule, their
work is marked by so impersonal a physiognomy, is so much the
outcome of certain preconceived and rigid conventions, that one
could almost believe them inspired by the same mind, and done by
the same hand.
Whilst French influence reigned almost supreme in Germany and
the Low Countries, and Italian art became more and more the slave
of routine, English engraving had not yet begun to feel the influence
of the progress elsewhere achieved since the beginning of the
century. The time was, however, at hand when, in the reign of Louis
XV., London engravers who came to study in Paris should return to
their own country to practise successfully the lessons they had
learned. We must, therefore, presently turn to them; but, before
speaking of the pupils, we must briefly mention the achievements of
the masters, and narrate the story of French engraving in France
after the death of the excellent artists of the age of Louis XIV.

CHAPTER VIII.
ENGRAVING IN FRANCE AND IN OTHER EUROPEAN
COUNTRIES IN THE EIGHTEENTH CENTURY. NEW
PROCESSES: STIPPLE, CRAYON, COLOUR, AND AQUATINT.
Morin, Nanteuil, Masson, and the other portrait engravers of the
period, in spite of the variety of their talent, left their immediate
successors a similar body of doctrine and a common tradition. Now
the works of the painter Rigaud, whose importance had considerably
increased towards the end of the reign of Louis XIV., made certain
modifications of this severe tradition necessary on the part of the
artists employed to engrave them. Portraits, for the most part bust
portraits, relieved against an almost naked background, were no
longer in fashion. To render a crowd of accessories which, while
enriching the composition, frequently encumbered it beyond
measure, became the problem in engraving. It was successfully
solved by Pierre Drevet, his son Pierre Imbert, and his nephew
Claude Drevet, this last the author, amongst other plates now much
prized, of a Guillaume de Vintimille and a Count Zinzendorff.
The first of these three engravers—at Lyons the pupil of Germain
Audran, and at Paris of Antoine Masson—engraved, with some few
exceptions, only portraits, the best known of which are a full-length
Louis XIV., Louis XV. as a Child, Cardinal Fleury, and Count
Toulouse; they attest an extreme skill of hand, and a keen
perception of the special characteristics of the originals. The second,
the similarity of whose Christian name has often caused him to be
mistaken for his father, showed himself from the first still more skilful
and more certain of his own powers. He was only twenty-six when

he finished his full-length Bossuet, in which the precision of the
handling, the exactness and brilliancy of the burin work, seem to
indicate a talent already arrived at maturity. In this plate, indeed,
and in some others by the same engraver—as the Cardinal Dubois,
the Adrienne Lecouvreur, and others—there are parts, perhaps,
that seem almost worthy of Nanteuil himself. It is impossible to
imitate with greater nicety the richness of ermine, the delicacy of
lace, and the polish and brilliancy of gilding; but the subtle delicacy
of physiognomy, the elasticity of living flesh which animated the
portraits of the earlier masters, will here be looked for in vain. Such
work is the outcome of an art no longer supreme, albeit of a very
high order still.
As much may be said of the best historical plates engraved in
France under the Regency, and in the first years of Louis XV. The
older manner, it is true, was still perceptible, but it was beginning to
change, and was soon to be concealed more and more under a
parade of craftsmanship amusingly self-conscious, and an elegance
refined to the point of affectation.

Fig. 87.—LAURENT CARS.
L'Avare. From Boucher's Molière.
The French engravers of the time of Louis XV. may be divided
into two distinct groups: the one submitting to the authority of
Rigaud, and partially preserving the tradition of the last century; the
other, of greater numerical importance, and in some respects of
greater ability, but, in imitation of Watteau and his followers, seeking
success in attractiveness of subject, grace of handling, and the
expression of a general prettiness, rather than in the faithful
rendering of truth.
As we know, the manners of the time were not calculated to
discourage a like tendency, which, indeed, grew more and more

general amongst artists during the whole course of the eighteenth
century, until it ended in a revolution, as radical in its way as the
great political one: namely, the exclusive worship of a somewhat
barren simplicity and of the antique narrowly understood.
In 1750 (that is to say, almost at the very time of the birth of
David, the future reformer of the school) the public asked nothing
more of art than a passing amusement. The immediate successors
of Lebrun had brought the historical style into great disrepute.
People had wearied of the pompous parade of allegory, the tyranny
of splendour, the monotony of luxury; they took refuge in another
extreme—in the exaggeration of grace and all the coquetries of
sentiment. Pastorals, or would-be pastorals, and subjects for the
most part mythological, took the place of heroic actions and
academical apotheoses. They had not a whit more nature than these
others, but they had at any rate more interest for the mind, and
greater charm for the eye.

Fig. 88.—LAURENT CARS.
Le Dépit Amoureux. From Boucher's Molière.
From the point of view of engraving alone, the prints published
in France at this time are for the most part models of spirit and
delicacy, as those of the Louis XIV. masters are of learned execution
and vigorous conception. Moreover, under the frivolous forms
affected by French engraving in the eighteenth century, something
not unfrequently survives of the masterly skill and science of the
older men. It is to be supposed that Laurent Cars remembered the
example of Gérard Audran, and, in his own way, succeeded in
perpetuating it when he engraved Lemoyne's Hercule et Omphale,
and Délivrance d'Andromède. Even when he was reproducing such

fantasies as the Fête vénitienne of Watteau, or scenes of plain
family life, like Chardin's Amusements de la Vie privée, and La
Serinette, he had the art of supplementing from his own taste
whatever strength and dignity his originals might lack. Was it not,
too, by appropriating the doctrine, or at least the method, of Audran
—his free alliance of the burin with the needle—that Nicolas de
Larmessin, Lebas, Lépicié, Aveline, Duflos, Dupuis, and others,
produced their charming transcripts of Pater, Lancret, Boucher
himself—in spite of his impertinences of manner and his unpleasant
falseness of colour—and, above all, Watteau, of all the masters of
the eighteenth century the best understood and the most brilliantly
interpretated by the engravers? A while later, Greuze had the honour
to occupy them most; and some among them, as Levasseur and
Flipart, did not fail to acquit themselves with ability of a task
rendered peculiarly difficult by the flaccid and laboured execution of
the originals.

Fig. 89.—CHEDEL.
Arlequin Jaloux. After Watteau.
However summary our description of the progress of French
engraving during the whole of the reign of Louis XV., or the early
years of Louis XVI., it is scarcely possible not to mention, side by
side with historical and genre engraving, the countless illustrations—
of novels, fables, songs, and publications of every description—the
general aspect of which so strongly bears witness to the fertility and
grace of French art at that time. It is difficult to omit the names of
those agreeable engravers of dainty subjects, not seldom of their
own design: those poetæ minores, the vaudevillists of the burin,
who, from the interpreters of Gravelot, Eisen, and Gabriel de St.

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