2. Destructive and Nondestructive Tests
Applicable to Metals
Metals are tested for one or more of the following
purposes:
a)To assess the fundamental mechanical properties
b)To determine data values, to draw up
specifications for design
c)To determine the surface and sub-surface defects
in raw materials and processed parts
d)To check chemical composition
e)To determine the suitability of a material for a
specific application
3. Types of Tests for Metals
There are two types of tests for metals
i) Destructive tests
ii) Non-destructive tests
Destructive Tests
Used to measure the physical and mechanical properties of
metals. After testing, the component or specimen either breaks
or remains no longer useful for future use.
Examples- Tensile test, Impact test, Hardness test, Torsion test,
Fatigue test etc.
4. Types of Tests for Metals
Non-destructive Tests
A non-destructive test (NDT) is an examination of an object in
any mean which will not harm or destroy the future usefulness of
the test piece. It can be used for the purpose for which it was
made. It is mainly used to detect the defects of the material.
Examples- Radiography (X-ray, Gamma-ray), Magnetic particle
inspection, Dye penetrant inspection, Fluorescent penetrant
inspection, Ultrasonic inspection, Holography etc.
5. Types of Destructive Tests for Metals
i) Tensile Test
ii) Compression Test
iii) Impact Test
iv) Hardnes Test
Tensile Test: Most widely used mechanical test. Used to
determine tensile properties, such as Tensile strength,
Yield point or Yield strength, % elongation, % reduction
in
area, modulus of elasticity etc. Universal Testing Machine
(UTM) is used.
7. Types of Destructive Tests for Metals
Compression Test: Used to determine the compressive
strength. Here also UTM is used. Not used so widely for metals.
Impact Test: It is essential in order to study the behavior under
dynamic loading. In Impact test, a specimen, notched, is struck
and broken by a single blow in a specially designed Impact
testing machine.
Two types of specimen are used: a) Charpy and b) Izod
9. Types of Destructive Tests for Metals
Hardness Test: Hardness is not a
fundamental property of metal, but
is related to the elastic and plastic
properties. The test procedure and
sample preparation are simple.
Results may be used to estimate
other mechanical properties.
Widely used for inspection and
control. Heat treatment and
working usually change the
hardness.
10. Non Destructive Tests for Metals
NDTs are Used to Detect
• Faulty components/parts before assembly
• To measure thickness of materials
• To identify or sort materials
• To discover defects that may have developed
during processing and use
• Parts may also be tested in service, permitting their
removal before failure occurs
Importance:
NDT is essential in industries like aerospace, automotive,
construction, and manufacturing for ensuring the safety,
reliability, and longevity of metal components.
11. Common NDT methods used for metals
1. Ultrasonic Testing (UT)
2. Radiographic Testing (RT)
3. Magnetic Particle Testing (MPT)
4. Eddy Current Testing (ECT)
5. Liquid Penetrant Testing (LPT)
6. Visual Inspection (VI)
7. Acoustic Emission Testing (AET)
8. Thermography
12. Ultrasonic Testing
Ultrasonic Testing (UT) is a widely used non-destructive testing
(NDT) method that employs high-frequency sound waves to
detect flaws, measure thickness, and evaluate the properties of
metals.
Principle:
UT relies on the transmission of high-frequency sound waves
(typically between 1 to 10 MHz) into the metal being tested. These
sound waves travel through the material and are reflected back by
internal structures, boundaries, or flaws such as cracks, voids, or
inclusions.
The time it takes for the sound waves to return and the intensity of
the reflection provide information about the location and size of
13. Radiographic Testing
A radiograph is a shadow picture of a material. The rays
darkens the film so that regions of lower density which readily
permit penetration appears dark on the negative as compared
with regions of higher density. Thus, a hole or crack
appears as a darken area.
The radiography of metals may be carried out by using x-rays
or gamma-rays capable of going through relatively large
thickness of metals.
a) X-ray Radiography
b) Gamma-ray Radiography
14. Radiographic Testing
Principle:
RT involves directing a beam of X-rays or gamma rays
through the material. As the radiation passes through the
object, it is absorbed at different rates depending on the
material's thickness and density.
A detector (traditionally a film, but more commonly now a
digital detector) is placed on the opposite side of the material
to capture the radiation that passes through. This creates an
image or radiograph that reveals internal features, including
any defects.
15. Differences between X-ray and Gamma-
ray
X-ray Gamma-ray
X-rays are potentially
dangerous for human body.
More penetrating than x-rays,
used for thicker objects
Produce better result Inferior in sensitivity
Better for detecting small
defects
No way to regulate the
contrast or variable thickness
Rapid, less time of exposure
Require much longer
exposure time
Costly and complicated
apparatus
Small equipment, suitable for
field inspection, portable
Can inspect one item at a
time
Can inspect a number of items
at a time
16. Magnetic Particle Inspection Testing
Magnetic Particle Testing (MPT), also known as Magnetic
Particle Inspection (MPI), is a non-destructive testing (NDT)
method used to detect surface and near-surface defects in
ferromagnetic materials like iron, steel, nickel, and cobalt.
MPT is widely used in industries such as aerospace,
automotive, oil and gas, and manufacturing to inspect
components like castings, forgings, and welds for cracks,
seams, and other discontinuities.
17. Magnetic Particle Inspection Testing
Principle:
•When a material is magnetized, magnetic lines of force, called
magnetic flux, flow through the material. If there is a
discontinuity, such as a crack, it will cause a distortion in the
magnetic field, leading to a leakage field at the surface.
•Finely ground magnetic particles (either dry powder or
suspended in a liquid) are then applied to the surface of the
material. These particles are attracted to the leakage fields,
accumulating around the defect and forming a visible indication.
18. Liquid Penetrant Testing
Liquid Penetrant Testing (LPT), also known as Dye Penetrant
Inspection (DPI) or Penetrant Testing (PT), is a non-destructive
testing (NDT) method used to detect surface-breaking defects in
non-porous materials, such as metals, plastics, and ceramics.
a) Liquid dye penetrant inspection
b) Fluorescent penetrant inspection
19. Liquid dye penetrant inspection
• Used to detect defects that are open to surface.
• Ex- cracks, seams, laps, porosity etc.
Procedure
Clean the surface to remove dust and dirt with a piece
of cloth
Brush the surface to remove scale, rust, paint etc. by a
soft brush
Spray a cleaner to remove oil, grease etc.
Apply the dye penetrant to cover the area to be tested
adequately. Allow 3-5 min. or more for the dye to
penetrate into the defects.
20. Liquid dye penetrant inspection
Again spray a cleaner to remove the remaining dye
Spray the developer evenly on the surface to give a
thin layer. The layer absorbs the penetrant from the
defects appearing on the surface to give a visible
indications of the defects.
The defects if any will be indicated by red dye
absorbed by the white developer (absorbent)
21. Fluorescent penetrant inspection
It is also used to detect small surface cracks.
Procedure
Clean the surface
Apply the fluorescent penetrant on the surface. Allow the
penetrant for one hour. The
fluorescent penetrant is drawn into the cracks by capillary
action
Wash the surface with water spray to remove penetrant
from surface but not from cracks
Apply the developer to draw the penetrant out of cracks
and enlarged in size
The surface is viewed under black lights (ultraviolet ray).
Black light causes penetrant to glow in dark.
22. Eddy Current Inspection
Eddy Current Inspection (ECT) is a non-destructive testing (NDT)
method used to detect surface and near-surface defects in
conductive materials, primarily metals.
Principle:
ECT is based on electromagnetic
induction. When an alternating current
flows through a coil, it generates a
changing magnetic field around the coil.
If the coil is brought near a conductive
material, this magnetic field induces
circulating currents within the material,
known as eddy currents.
23. Eddy Current Inspection
These eddy currents generate their own magnetic field, which
opposes the original magnetic field from the coil. The
interaction between these fields changes the coil's impedance
(resistance and inductance).
Any discontinuity, such as a crack or a change in material
properties, will disrupt the flow of eddy currents, leading to a
detectable change in the coil's impedance. By analyzing these
changes, defects and other material properties can be identified.
24. Eddy Current Inspection
These eddy currents generate their own magnetic field, which
opposes the original magnetic field from the coil. The
interaction between these fields changes the coil's impedance
(resistance and inductance).
Any discontinuity, such as a crack or a change in material
properties, will disrupt the flow of eddy currents, leading to a
detectable change in the coil's impedance. By analyzing these
changes, defects and other material properties can be identified.
