TALAT Lecture 2205: Special Design Issues

TALAT Lecture 2205

Special Design Issues
24 pages, 31 figures

Basic Level

prepared by Torsten Høglund, Royal Institute of Technology, Stockholm
Dimitris Kosteas, Technical University, Munich
and
Steinar Lundberg, Hydro Aluminium Structures, Karmoy

Objectives:

− to describe the measurement and amount of residual stresses in extruded and welded
profiles which have to be accounted for in design
− to introduce the subject of corrosion and of preventive design measures
− to describe the behaviour and properties of structural aluminium alloys at ambient,
low and elevated temperatures
− to give useful examples of structural applications of extrusions

Prerequisites:

− background in mechanical and structural engineering disciplines

Date of Issue: 1994
 EAA - European Aluminium Association

2205 Special Design Issues

Table of Contents

2205 Special Design Issues ...................................................................................2
2205.01 Residual Stresses ....................................................................................... 3
Introduction..............................................................................................................3
How to Measure Residual Stresses ..........................................................................4
Residual Stress in Extruded Profiles........................................................................4
Residual Stresses in Welded Profiles.......................................................................6
Residual Stress Effects on Fatigue Behaviour .........................................................8
2205.02 Corrosion ................................................................................................. 10
Introduction............................................................................................................10
Galvanic Corrosion ................................................................................................11
Differential Aeration Corrosion.............................................................................12
Design Examples for Avoiding Corrosion.............................................................13
2205.03 Working Temperature............................................................................. 18
Mechanical Properties............................................................................................18
Aluminium Alloy Structures Exposed to low Temperatures .................................19
Aluminium Alloy Structures Exposed to Elevated Temperatures. ........................20
Linear Thermal Expansion.....................................................................................20
2205.04 Using Extrusions in Design .................................................................... 21
2205.05 References................................................................................................ 23
2505.06 List of Figures............................................................................................ 23

TALAT 2205 2

2205.01 Residual Stresses

• Introduction
• How to measure residual stresses
• Residual stress in extruded profiles
• Residual stresses in welded profiles
• Residual stress effects on fatigue behaviour

Introduction

If a part of a structural element has been subjected to non-uniform, plastic deformation,
residual tension and compression stresses will remain which are within the elastic
regime. The sum of internal tension and compression stresses is always zero, if there are
no external forces. The inhomogeneous deformation field which generates residual
stress is caused by processes such as cooling and quenching after extrusion, welding or
cold working, e.g. bending and straightening of profiles.

For a welded T-profile the residual stresses may develop as follows: During
solidification and further cooling the material of the weld zone experiences a larger
shrinkage than the surrounding colder and more rigid base metal due to volume
differences in the liquid and solid states and due to thermal contraction. The larger
shrinkage of the weld zone induces tensile stresses in a magnitude limited by the
momentary yield strength of the material in the warmer weld zone. The contraction of
the weld and heat affected zone induces in turn compressive stresses in the the cross
section of the surrounding colder base material, see Figure 2205.01.01.

Example of Residual Stresses in a Welded T-Profile

+

-

+

-
alu

Training in Aluminium Application Technologies
Example of Residual Stresses in a Welded T-Profile 2205.01.01

TALAT 2205 3

How to Measure Residual Stresses

The most common method is the destructive method which is based upon the technique
of cutting the specimen in a number of strips (Figure 2205.01.02). The residual stresses
are calculated from measurements on each strip.

There are two methods of measuring. The first is to measure the length of the strip
before and after cutting it from the section. If Young's modulus is known, it is easy to
apply Hooke's law and determine the residual stress. The second method is to mount
electrical resistance strain gauges on the strips and determine the residual stresses by
applying Hooke's law. This method is the most commonly used one today. Note:
Hooke's law can be applied since residual stresses are essentially within the elastic
range. With the methods stated here only longitudinal residual stresses are determined,
which, however, are of greatest importance from a structural point of view.

Residual Stress in Extruded Profiles

Mazzolani | 1 | shows results from a number of experiments where residual stresses were
determined for different types of profiles. These consist of different alloys and were
manufactured by various processes. The results from experiments on I-profiles are
shown in Figure 2205.01.01 and Figure 2205.01.02.

Sectioning a Test Beam For Measuring of
Residual Stresses
b

L0
L1

L

h

alu Sectioning a Test Beam For Measuring of
2205.01.02
Residual Stresses

The results of experiments conducted on I-profiles consisting of four different alloys are
shown in Figure 2205.01.03. The residual stresses seem to be randomly distributed over
a cross section. No simple rule seems to apply to the stress distribution as is the case for
rolled steel sections. Observations show that residual stresses are low, the compressive

TALAT 2205 4

stresses almost never exceed 20 MPa and tensile stresses are much lower. These values
are measured on the surface of the profiles. At the center of the material the values are
probably even lower, since residual stresses usually change sign from one side to the
other.

Residual Stresses in an I-Profile of Different Alloys

1 A - U4G ; f0.2 = 40.5 ; ft = 50.7 ; ετ = 13.8
2 A - GSM ; f0.2 = 13 ; ft = 28.5 ; ετ = 31
3 A - SGM ; f0.2 = 27.6 ; ft = 30.4 ; ετ = 17.7
2 A - Z5G ; f0.2 = 27.5 ; ft = 34 ; ετ = 10 4
+ 4 +

1 3
+ +
+ + + +
Scale: 50 N/mm²

+ tension
compression
1 2 3 4
+ +
1 3
+ 2 + 4

Source: Mazzolani

alu
Residual Stresses in an I-Profile of Different Alloys 2205.01.03

The intensity and distribution of residual stresses in aluminium profiles seem to be not
affected by alloy composition.

Figure 2205.01.04 shows the results of experiments on an I-profile at different stages in
the manufacturing process.

3 Alloy 7020
+
1. Extruded and cooled by air
2
+ 2. Extruded and straightened (about 1%)
1
3. Extruded, straightened and artificially
+
tempered (100° C for 4 hours and
+ + +
140° C for 24 hours).

1 2 3
+
1 Scale: 50 N/mm²
+ 2 + tension
compression
+
3

Source: Mazzolani

alu Residual Stresses in I-Profiles for Different
2205.01.04
Manufacturing Processes

TALAT 2205 5

The residual stresses for these cases are rather small and seem to change from
compression to tension during refinement. The reduction of residual stresses is due to
the straightening process that the profiles are subjected to during manufacturing. The
remaining residual stresses have a negligible effect on the load bearing capacity.

Residual Stresses in Welded Profiles

In contrast to what has been said for extruded profiles, residual stresses cannot be
neglected in welded profiles. Welding produces a concentrated heat input which causes
the remaining stresses (see above). Large tensile stresses in connection to the web and
balancing compression stresses in other parts are characteristic.

Figure 2205.01.05 shows the results of residual stress measurements for an I-beam
fabricated by welding aluminium plates of different sizes and alloys. Both, heat-treated
and non-heat-treated alloys were used. The resulting differences were very small. The
maximum tensile stress was 90 - 100 N/mm² and the maximum compression stress 30 -
40 N/mm². The lower values correspond to the heat-treated alloy.

σr(N/ mm )
2

150
100
50
+
0
-
50
100

σr(N/ mm )
2
150 100 50 0 50 100 150
150
+ -
100

50
+ 0
- 50

σr(N/ mm )
100 2
Source: Mazzolani

alu Typical Residual Stress Distribution for a 2205.01.05
Training in Aluminium Application Technologies Welded I-Profile Consisting of Flat Plates

Typical residual stress distributions for two different I-profiles are shown in Figure
2205.01.05 and Figure 2205.01.06. The highest values of tensile stress in both cases
were 140 N/mm². The greatest values of compressive stresses were 50 N/mm² except for
the web of the specimen in Figure 2205.01.06 where compressive stresses reached 100
N/mm². An important conclusion reached from these experiments is that welded
connections between extruded profiles should be placed in areas where they cause a
minimum reduction of strength.

TALAT 2205 6

These experiments also show that the residual stresses in relation to the yield limit of the
material are much lower for aluminium profiles than for corresponding steel profiles. In
the experiments, the residual tensile stresses were less than 60 % of the 0,2 % proof
stress. For steel residual stresses may be greater than the yield stress of the material. The
residual compressive stresses are typically 20 % for aluminium and 70 % for steel.
Therefore, considering residual stresses, it is more favourable to weld aluminium than it
is to weld steel. However, for aluminium the strength of the material is reduced up to 50
% in the zone around the weld. This counterbalances the effect of the residual stress
distribution.

σr(N/ mm )
2
100
+ 50
- 0
50
100

σr(N/ mm )
2
150 100 50 0 50 100 150
100
+ -
50
+
- 0
50
100
σr(N/ mm )
2
Source: Mazzolani

alu Typical Residual Stress Distribution For an I-Profile
2205.01.06
With Flanges Consisting of Extruded Profiles

In order to take residual stresses into consideration when solving numerical problems.
e.g. in stability problems, the stress distribution is approximated for different cross
sections (Figure 2205.01.07).

σr σr
f0.2 fy

1.0
0.6 +
0.2 0.7
- -
0.5 0.6 σr
f0.2

+

-

+

σr
fy
0.6 1-1.50
Steel Fe 360 (fy = 235 N/ mm2)
Alloy 6082 (f0.2 = 235 N/ mm2)

alu
Example of Approximated Residual Stress Distribution 2205.01.07

TALAT 2205 7

The stress distribution model is convenient when simulating problems by use of
computer calculations.

Normally, a further simplification is adopted. Often the continuous curves are replaced
by equivalent block curves as those shown in Figure 2205.01.08. These curves are
easier and faster to use in numerical models. The last type is the one used for the
determination of load-bearing curves for design regulations.

σf- = 50 N mm2
b = 100mm
σf = σw = 140 N mm2
+ +
N mm2 χb χb
σw =120 N mm2
-
150
100

+
50 σf
+
χ = 0,30
0
ξ
h
-
50 σf
-
= 0,157
σ w
+
σw
-

100

12
ξh
200 mm

8
h = 176mm

ξh

N mm2
150 100 50 0 50 100 150
+ -

alu Example of the Most Common Way of Determining 2205.01.08
a Residual Stress Distribution.

Residual Stress Effects on Fatigue Behaviour

Earlier we have already mentioned the difficulties in detecting, measuring or in any way
quantifying the residual stress situation of a structural component. Indirectly, this
situation has been reflected in the proposals for the „fatigue reduction factor“ f(R).

Currently efforts are being undertaken to quantify the residual stress pattern of welded
aluminium constructions. During the course of the drafting of the ECCS-ERAAS
(European Recommendation for Aluminium Alloy Structures) information was used
which was obtained from the comprehensive welded-beam fatigue testing programmes
at the Technical University of Munich (TUM). Residual stress measurements were made
of full-size welded components of 7020 and 5083 alloys, see Figure 2205.01.09.

The measurements themselves and the difficulties associated with the interpretation of
these limited results together with other somewhat contradictory information being
described elsewhere allow presently only the following general conclusions:

− Residual stresses in welded components of aluminium are of considerable magnitude,
reaching values up to the 0,2 - yield limit of the HAZ, see Figure 2205.01.10

TALAT 2205 8

− Scatter is an inherent feature in measurements made by the hole-drilling method.
Efforts were undertaken to make measurements sufficiently close to the welds,
approximately 1 mm off the weld toe, by using rosettes with the strain gages arranged
on one side only.

− There were some but not significant differences in residual stresses in the structural
details of the 7020 and 5083 alloy.

0
B2 •10•27
0
12

0
B1 •10•24 40
0
0
12
C4
B2 12
00

C2
C1 40
0 B2

0
C3 40
0
B2 40
00
0 B1 12
40
0
40
B1 D2 15•300 00
40
0 0• 12
15
1
/ E 350 40
0
E2 50•30•
3 0
00 40
12 D1 300
5•
0•1
15 40
0

40
0 B2 40
0

0
40

0
40
B1
0
40

00
12

00
12

Source: D. Kosteas, Technical University Munich

alu
Welded Aluminium Beams for Fatigue Tests 2205.01.09

As seen in Figure 2205.01.10 the highest values of residual stresses were recorded at
fillet welded longitudinal or transverse attachments on the beam flanges. Residual
stresses in these details reached values of over 180 MPa. Residual stress measurements
at butt welded splices and cruciform joints made with butt-like full penetration welds
attained values of between 120 and 140 MPa.

No answer can be offered for the time being to the question of whether initially
measured residual stresses are maintained, and at what magnitude, during subsequent
load cycling of the components. Indirect measurements at strain gauge monitored crack
initiation sites showed values up to 120 MPa. These gauges may not have been
sufficiently close to the maximum residual stress site, though. Residual stresses,
therefore, may have been higher.

The generally lower level and steeper slope of S-N curves of full-size components vs.
small specimen data agree with similar findings in steel weldments (see DIN 15015 and
Eurocode 3 or ECCS TC6).

There are still difficulties in interpreting differences between S-N curves with stress
ratios of R = -1 and +0,1. The first show at times approximately 40 % higher fatigue
strength values of stress range plotted in a log-log diagram at two million cycles. The

TALAT 2205 9

effect is more pronounced in the case of 7020 alloy details. It does not seem prudent,
though, to allow for a bonus in design values in cases of large components, since
sufficiently reliable data is still missing.

HAZ yield strength design value

200
HAZ
R = 180
p0,2

150
R HAZ = 125
p0,2
100
Residual Stress σ z

50
in tension N/ mm2

0
B C1 C2 C3 C4 D1 D2 E
V X
X V V X

7020 5083
σx
Residual Stress σ1 = from 1.20 to 1.60 σz σ1 σz

Source: D. Kosteas, Technical University Munich

alu
Residual Stresses Measured in Fatigue Test Beams 2205.01.10

2205.02 Corrosion

• Introduction
• Galvanic corrosion
• Differential aeration corrosion
• Design examples for avoiding corrosion

Introduction

Aluminium and its alloys are always protected by a film of Al2O3 or Al2O3 · H2O of
various thicknesses due to their large oxygen affinity. Due to this protective film, the
alloys have a good resistance to sea water, most neutral solutions, many weak acid
solutions as well as sulfurated hydrogen, hydrocarbons and carbonic acid. The pH has to
be between 4,5 and 9,0 if inhibitors are not added.

Aluminium is a metal with a large electronegative potential. Contact between
aluminium and more electropositive metals such as copper, lead and steel when

TALAT 2205 10

moisture is present, must be avoided. This can be done by using correct electrical
insulation between the two metals, i.e. by use of neoprene, plastic or equivalents.

However, in certain conditions, the use of stainless steel bolts or explosion welded
plates as connection can be accepted due to the mass and passivation effect.

Because of the protective film on the aluminium surface, no painting is needed, leaving
aluminium almost maintenance free in many environments.

The causes for corrosion damages can be avoided in the design phase. Two types of
corrosion are of particular importance when designing an aluminium alloy structure for
a corrosive environment:
− galvanic corrosion
− differential aeration corrosion

Galvanic Corrosion

When aluminium alloys are in electrical contact with more electropositive metals and
submerged in a corrosive electrolyte, galvanic corrosion will take place. To avoid this
type of corrosion, therefore, the flow of current has to be interrupted by insulating the
two dissimilar metals and the surface has to be protected against the electrolyte.

An example ist given in Figure 2205.02.01 which shows an aluminium alloy/steel
connection. Bolting aluminum alloy to aluminium alloy, stainless steel bolts (A4
quality) may be used without any insulation, except when the connection is permanently
submerged in water or in another fluids which will act as electrolyte. This solution has
proved to be acceptable through many years of experience in the North Sea oil industry
(Helideck structures).

3
5
4

2
1

1) Aluminium alloy 4) Nylon collar

2) Steel 5) Stainless steel

3) Neoprene Gasket

alu Methods For A Bolted Connection Between Steel and
Aluminium Alloy for a Corrosive Environment
2205.02.01
Training in Alum inium Application Technologies

TALAT 2205 11

When designing bolt connections with gaskets and collars, one should be aware of the
weakness of both, the gasket and the collar. The shearforces of such a connection must
be small to avoid damages of the collar and electrical contact between bolt and metal.
The best solution for an insulated bolted connection is to transmit the forces through the
connection by compression.

Connections between steel and aluminium will be dependent on the environments.
Figure 2205.02.02 (table) shows four different methods for connections in six different
environments.

Stainless steel Stainless steel
Explosion- bolts, neoprene bolts, neoprene No
Environments welded gaskets, nylon gaskets, no precautions
joints, painted collar collars
Sea water no yes no no
immersion
Humid marine
atmosphere yes yes no no
Aerated
marine yes yes yes no
atmosphere
Industry
pollution yes yes yes no
atmosphere
Rural
atmosphere
Condensed/ yes yes yes no
fresh water
immersion
Indoor
atmosphere yes yes yes yes
RH < 60 %
alu Connections Between Steel and Aluminium
Training in Aluminium Application Technologies in Six Different Environments 2205.02.02

Differential Aeration Corrosion.

This type of corrosion occurs when an oxygen concentration gradient exists in the
electrolyte in contact with the metal surface.

Differential aeration corrosion may take place in crevices filled with water, spaces filled
with stillstanding water or areas covered by wet materials.

In the design phase many of these corrosion problems can be solved. Some simple rules
are as follows:

• Avoid crevices which can be filled with water or other liquids acting as an
electrolyte. Crevices should be permanently sealed.

• Avoid structural details or cross sections which collect stillstanding water or other
corrosive liquids. If such details cannot be avoided, they must be drained properly.

TALAT 2205 12

• Avoid structural details or cross sections which will collect dirt. If this is impossible,
design a detail which is easy to clean.

• Do not use insulation materials which are porous and absorbent between metal
surfaces.

• Do not cover aluminium surfaces with porous and absorbent materials which can get
wet.

Design Examples for Avoiding Corrosion
(Figures 2205.02.03 till 2205.02.12)

Bad (left) and Recommended Designs (right)
for Drainage of Containers

alu Bad (left) and Recommended Designs (right)
Training in Aluminium Application Technologies for Drainage of Containers 2205.02.03

Tanks must be designed in such a way that cleaning and draining are easily achieved
(Figure 2205.02.03). Profiles exposed to moisture must be arranged in such a way that
they will be drained and cleaned easily (Figure 2205.02.04).

Bad and Recommended Designs
for Drainage of Profiles

Bad Acceptable Good

alu Bad and Recommended Designs
Training in Aluminium Applicat ion Technologies for Drainage of Profiles 2205.02.04

TALAT 2205 13

Often humidity collects around cold spots in poorly insulated structures, e.g. on a pipe
or tank containing warm and humid gas. Figure 2205.02.05 shows the recommended
solution (at right).

Condensation leads
to corrosion

When supporting a pipe or a tank containing warm and humid gas, the
support also has to be insulated. The right solution is recommended.

alu

Avoiding Corrosion by Condensation at Cold Spots 2205.02.05

Particular attention should be given to crevice corrosion at connections or joints. Figure
2205.02.06, Figure 2205.02.07 and Figure 2205.02.08 show examples of good and bad
solutions with respect to crevice corrosion at bolted and welded connections.

overlap
d crevice
c
a

crevice

b e

Examples of good and bad solutions regarding crevice corrosion

a) avoid porous and absorbent material as gaskets
b) aim at exactly cut gaskets
c) & d) when welding avoid crevice
e) use buttweld instead of overlap

alu Examples of Good and Bad Solutions With Respect to
2205.02.06
Crevice Corrosion at Bolted and Welded Connections

TALAT 2205 14

Avoiding Unfavourable Fillet Welds and Fillet Welds
With Difficult Accessibility

alu Avoiding Unfavourable Fillet Welds and Fillet Welds
Training in Aluminium Application Technologies With Difficult Accessibility 2205.02.07

Avoiding Crevice Corrosion at Beam

Crevice between crossing beams can be avoided if the upper beam
has shape as shown on the sketch.

alu

Avoiding Crevice Corrosion at Beam 2205.02.08

Aluminium tube Copper tube

Cu+

Cu
Cu+

Example of galvanic corrosion with precipation of Cu-ions in a pipe of
aluminium alloy. If the stream is opposite, there is no corrosion problem.

alu Galvanic Corrosion Caused by Precipitation of
Training in Aluminium Application Technologies Cu - Ions in an Aluminium Pipe 2205.02.09

Special care should be given to galvanic corrosion problems when dissimilar metals are
joined together. Figure 2205.02.09 shows an example of a pipe connection between
aluminium and copper. Despite perfect insulation copper-ions can precipitate on the

TALAT 2205 15

walls of the aluminium pipe if the fluid flow direction is from right to left (Figure
2205.02.09). If the flow direction is opposite no corrosion will occur.

Explosion Welded Connections Between Steel
and Aluminium Alloy

Aluminium

Steel

alu Explosion Welded Connections Between Steel
2205.02.10
Training in Aluminium Application Technologies and Aluminium Alloy

Explosion welded connections between steel and aluminium alloys have successfully
been used in the ship building industry for many years. To avoid corrosion at such
dissimilar metal connections protective painting is recommended. the arrangement of
the aluminium/steel connection on a steel deck is shown in Figure 2205.02.10. Even
though, the distance x should be sufficiently large avoiding continuous wetting of the
aluminium structure by sea water on deck (Figure 2205.02.11).

Recommendations for Corrosion Prevention on
Aluminium/ Steel Structures on Ship Decks

Outside

Sealant

Steel

x
Deck

alu Recommendations for Corrosion Prevention on
2205.02.11
Training in Aluminium Application Technologies Aluminium/ Steel Structures on Ship Decks

Bolted connections should be designed with full electrical insulation. Stainless steel
bolts are recommended. In a dry atmosphere galvanized bolts will perform satisfactorily.
Figure 2205.02.12 gives an example for a flange connection between two dissimilar
metals.

TALAT 2205 16

1

3

2

1. Insulation material
2. Gasket
3. Stainless steel bolt or in dry atmosphere galvanized bolt

alu
Flange Connection Between Two Dissimilar Metals 2205.02.12

Figure 2205.02.13 gives an example for a corrosion resistant bolted connection between
aluminium and steel. It is recommended to seal the flange edges of the connection with
an elastic, non conducting sealant. The danger of corrosion is reduced when the distance
between neighbouring surfaces of the two dissimilar metals is as large as possible

Example of a bolted connection between
steel and aluminium
Outside
6

1. Bolt of stainless steel or
Aluminium
galvanized steel

2. Nut of stainless steel or
galvanized steel
b

d1

3. Spring washer

4. Gasket of neoprene 5

5. Collar of nylon
4
1 2 3
6. Sealant

Steel
alu
Example of a Bolted Connection Between Steel and Aluminium 2205.02.13

TALAT 2205 17

2205.03 Working Temperature

• Mechanical properties
• Aluminium alloy structures exposed to low temperatures
• Aluminium alloy structures exposed to elevated temperatures
• Linear expansion

Mechanical Properties

The strength of aluminium alloys is highest at absolute zero and decreases as the
temperature up to the melting point (Figure 2205.03.01). The variation of strength
depends on the type of alloy and temper. At low temperatures aluminium alloys have no
tendency to brittleness which occurs in many steels.

Strength in MPa A5 in %
400 60

300 50

Elongation
200 40 of rupture

Ultimate
30 strength
100
Yield strength

20
-200 -100 0 100 200
Temperature in deg. Celsius

alu Effect of Temperature on Strength and
Training in Aluminium Application Technologies Elongation of 5083 - H112 2205.03.01

The tables in Figure 2205.03.02, Figure 2205.03.04 and Figure 2205.03.04 show in
percentage the variation of strength, Young’s modulus of elasticity and the elongation of
rupture (A5) between - 200 °C and + 200 °C for some alloys.

TALAT 2205 18

Aluminium Alloy Structures Exposed to low Temperatures

Low temperatures have the effect of improving the mechanical properties and often also
the toughness of aluminum alloys without any tendency to brittleness.

Alloy and Yield strength in % at various temperatures in ° C
temper
-200 -100 +25 +100 +200
5052-H34 115 100 100 100 50
5083-H112 120 115 100 95 55
5454-H32 115 105 100 95 70
6061-T6 135 105 100 95 40
6063-T6 115 105 100 95 20
6082-T6 115 105 100 95 40

Source: C. Marsh, Alcan Canada Products Ltd., 1983

alu Yield Strength in % for Some Alloys in the
2205.03.02
Training in Aluminium Application Technologies Temperature Range From -200 to +200 °C

Young´s Modulus of Elasticity in % in
the temperature range from -200 to +200 °C

-200 -100 +25 +100 +200

Elastic
Modulus 110 105 100 100 90

Source: C. Marsh, Alcan Canada Products Ltd., 1983

alu Young´s Modulus of Elasticity in % in the Temperature
2205.03.03
Training in Aluminium Application Technologies Range From -200 to +200 °C

Elongation of Rupture (A5) in % in the
Temperature Range From -200 to +200 °C

Alloy and
-200 -100 +25 +100 +200
temper

5052-H34 25 19 14 16 45
5083-H112 36 31 25 36 60
5454-H32 30 22 16 18 45
6061-T6 22 18 17 18 28
6063-T6 21 17 18 19 40
6082-T6 22 18 17 19 40

Source: Aluminium Taschenbuch, 14th Ed. Aluminium-Verlag, 1984

alu Elongation of Rupture (A5) in % in the Temperature
2205.03.04
Training in Aluminium Application Technologies Range From -200 to +200 °C

The heat affected zone of welded structures will also have an improvement of the
mechanical properties, but the elongation of rupture (A5) will usually be the same as at
room temperature.

TALAT 2205 19

Structures in aluminium alloys for low temperature conditions can, therefore, be
designed according to the codes and regulations applicable to normal, ambient
temperatures.
An explanation for the improved mechanical behaviour of aluminium structures at low
temperatures is that the difference between the ultimate strength and the yield strength
increase when the temperature decreases towards absolute zero. The safety factor
against fracture will for that reason increase with decreasing temperature. There is no
lower temperature limit for the application of structural aluminium alloys.

Aluminium Alloy Structures Exposed to Elevated Temperatures.

The strength of aluminium alloys decreases when the metal temperature increases
beyond room temperature. Most aluminum alloys suffer from considerable strength
reduction at temperatures between 120 - 250 °C.

Alloys which are age-hardened or strain-hardened will also loose some of their original
strength during a temporary period at elevated temperatures between 100 - 150 °C.

Under the prolonged application of a stresses of sufficient magnitude at elevated
temperatures, aluminium alloys will creep and may rupture after a period of time. This
behaviour does not enter into the design considerations for structures below 100 °C but
may require study for high temperature applications.

Maximum working temperatures for an aluminium alloy structure can be set to 100 °C.

Linear Thermal Expansion.

When aluminium alloy structures are connected to structures made of other material and
if they are subjected to larger temperature fluctuations, stresses caused by the
differences in linear thermal expansion must be taken into consideration. In the
temperature range from - 100 °C to 0°C the coefficient of linear thermal expansion can
be taken as 21,5 · 10-6 1/°C, in the temperature range 0°C to 100°C 23,5 · 10-6 1/°C can
be used as an average. When the relative difference in linear expansion is known,
Hooke’s law can be used to find the stress in the structure if the expansion will be
within the elastic range.

TALAT 2205 20

2205.04 Using Extrusions in Design

A great advantage in designing aluminium alloy structures is provided by the possibility
of using extruded sections. In Lecture 2202 some information is given about
availability, limitations and costs of extrusions. In Lecture 2302 "design of joints" a
number of examples illustrate the advantageous way of using extrusions in the design of
joints.

Structural applications sometimes require large members. If these members cannot be
produced from single extrusions, welding together smaller extrusions can be a good sol-
ution. The welds can than be located in places where the heat affected zones do not
reduce the bearing capacity of the member. Figure 2205.04.01 shows an I-beam made
of two identical extrusions, welded together with two buttwelds in the middle of the
web. The extrusions are produced ready for welding with the groove and backing
already attached in the extrusion process.

Large I-Beam Designed With Two
Identical Extrusions

alu

Large I-Beam Designed With Two Identical Extrusions 2205.04.01

Another way of making I-beams is shown in Figure 2205.04.02. The flanges are made
of extrusions and the web is a plate or an extruded flatbar. In such a way the same flange
extrusion can be used to make I-beams of different heights. This beam is welded
together with four fillet welds.

TALAT 2205 21

Large I-Beams Made of Extrusions and Plate

alu

Large I-Beams Made of Extrusions and Plate 2205.04.02

An example from a special case: A member must have bending stiffness horizontal in
the upper flange and vertical for the whole member. This is solved by using two
extrusions welded together with two buttwelds. Figure 2205.04.03 shows the solution.

Hollow Beam Design With High Bending Stiffness

alu

Hollow Beam Design With High Bending Stiffness 2205.04.03

In floor structures the extrusion technique can be used by extruding both the floor plate
and the stiffener in one extrusion. The extrusions can be put together in several ways:
welding, screwing, adhesive bonding or with snap connections, see Figure 2205.04.04.

TALAT 2205 22

Floor Extrusions joined together by

Welding

adhesive

Adhesive Bonding

Locking Screw

screw

alu

Floor Extrusions Joined by Various Methods 2205.04.04

2205.05 References

[1] Mazzolani, F.M.: Aluminium Alloy Structures. Pitman Advanced Publishing,
Program. 1985.

[2] ECCS-TC2: European Recommendations for Aluminium Alloy Structures -
Fatigue Design. 1992.

[3] SINTEF Korrosjonssenteret: Korrosjonshåndbok for aluminium. STF 34
A87116 (In Norwegian). 1987.

[4] Cedric March: Strength of aluminium. Alcan Canada Products Ltd. 1983.

[5] Aluminium-Taschenbuch, Aluminium-Zentrale e.V. (Herausgeber), Aluminium-
Verlag, Düsseldorf. 1984.

2505.06 List of Figures

Figure No. Figure Title (Overhead)
2205.01.01 Example of Residual Stresses in a Welded T-Profile
2205.01.02 Sectioning a Test Beam for Measuring of Residual Stresses
2205.01.03 Residual Stresses in an I-Profile of Different Alloys
2205.01.04 Residual Stresses in I-Profiles for Different Manufacturing Processes
2205.01.05 Typical Residual Stress Distribution for a Welded I-Profile Consisting of
Flat Plates.
2205.01.06 Typical Residual Stress Distribution For an I-Profile With Flanges
Consisting of Extruded Profiles

TALAT 2205 23

Figure No. Figure Title (Overhead)
2205.01.07 Example of Approximated Residual Stress Distribution.
2205.01.08 Example of the most Common Way of Determining a Residual Stress
Distribution.
2205.01.09 Welded Aluminium Beams for Fatigue Tests.
2205.01.10 Residual Stresses Measured in Fatigue Test Beams

2205.02.01 Methods for a Bolted Connection between Steel and Aluminium Alloy
for a Corrosive Environment
2205.02.02 Connections Between Steel and Aluminium in Six Different
Environments
2205.02.03 Bad (left) and Recommended Designs (right) for Drainage of Containers
2205.02.04 Bad and Recommended Designs for Drainage of Profiles
2205.02.05 Avoiding Corrosion by Condensation at Cold Spots
2205.02.06 Examples of Good and Bad Solutions with Respect to Crevice Corrosion
at Bolted and Welded Connections
2205.02.07 Avoiding Unfavourable Fillet Welds and Fillet Welds with Difficult
Accessibility
2205.02.08 Avoiding Crevice Corrosion at Beam
2205.02.09 Galvanic Corrosion Caused by Precipitation of Cu-Ions in an Aluminium
Pipe
2205.02.10 Explosion Welded Connections Between Steel and Aluminium Alloy
2205.02.11 Recommendations for Corrosion Prevention on Aluminium/Steel
Structures on Ship Decks
2205.02.12 Flange Connection Between Two Dissimilar Metals
2205.02.13 Example of a Bolted Connection Between Steel and Aluminium

2205.03.01 Effect of Temperature on Strength and Elongation of 5083 - H112
2205.03.02 Yield Strength in % for Some Alloys in the Temperature Range from -
200 to +200° C
2205.03.03 Young’s Modulus of Elasticity in % in the Temperature Range from -200
to +200° C
2205.03.04 Elongation of Rupture (A5) in % in the Temperature Range from -200 to
+200° C

2205.04.01 Large I-Beam Designed with two Identical Extrusions
2205.04.02 Large I-Beams Made of Extrusions and Plate
2205.04.03 Hollow Beam Design with High Bending Stiffness
2205.04.04 Floor Extrusions Joined by Various Methods

TALAT 2205 24

TALAT Lecture 2205: Special Design Issues

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