Chapter 4 - MATERIAL TESTING
Transcript of Chapter 4 - MATERIAL TESTING
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CHAPTER 4 : MATERIAL TESTING
JF302 –MATERIAL TECHNOLOGY 1
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MATERIAL TESTING
This topic provides an understanding on the purposes
of materials testing and deformities in certain
materials. It also explains on the definition and
principle on mechanical properties of materials,
destructive and non-destructive tests.
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4.0 MATERIAL TESTING – Summary
4.1 Describe material testing
4.1.1 Explain the purpose and types of
material testing deformation
4.1.2 Define mechanical properties in
material testing
a. Strength
b. Hardness
c. Elasticity
d. Plasticity
e. Ductility
f. Toughness
g. Brittleness
4.1.3 Define Destructive Test
4.1.4 Explain the principle of hardness
tests
a. Brinell Test
b. Vickers Test
c. Rockwell Test
d. Shore Test
4.1.5 Explain principle and results of
toughness tests
a. Izod Test
b. Charpy Test
4.1.6 Define Non-Destructive Test
4.1.7 Explain the methods for non
destructive test
a. Penetration test
b. Magnet powder test
c. Ultrasound test
d. X-ray test
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Purpose of Material Testing
Ensure quality (as aspect of control in production)
Test properties (mechanical properties)
Prevent failure in use (observed any defect in
component)
Make informed choices in using materials
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Types of Testing
1. Destructive testing – the material may be physically
tested to destruction. Will normally specify a value for
properties such as strength, hardness, toughness,
etc.
2. Non-Destructive – testing does not affect the
structural integrity of the sample. Samples or finished
articles are tested before being used. ( A
measurement that does not effect the specimen in
any way) e.g., liquid penetration, x-ray, etc.
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Mechanical Properties of Metals
• Strength
It is the ability of a material to resist the externally applied forces without breaking or yielding. The internal resistance offered by a part to an externally applied force is called *stress.
• Hardness
Hardness is the ability to withstand indentation or scratches by harder substances
• Elasticity
It is the property of a material to regain its original shape after deformation when the external forces are removed. This property is desirable for materials used in tools and machines. It may be noted that steel is more elastic than rubber.
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Mechanical Properties of Metals • Plasticity
It is property of a material which retains the deformation produced under load permanently. This property of the material is necessary for forgings, in stamping images on coins and in or namental work.
• Ductility
This is a property the metal contains which enables it to be drawn easily or stretched to a desired shape without fracturing, whilst retaining the shape. A ductile material must be both strong and plastic. The ductility is usually measured by the terms, percentage elongation and percentage reduction in area. The ductile material commonly used in engineering practice (in order of diminishing ductility) are mild steel, copper, aluminium, nickel, zinc, tin and lead.
• Toughness
It is the property of a material to resist fracture due to high impact loads like hammer blows. The toughness of the material decreases when it is heated. It is measured by the amount of energy that a unit volume of the material has absorbed after being stressed up to the point of fracture. This property is desirable in parts subjected to shock and impact loads.
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Mechanical Properties of Metals
• Brittleness
It is the property of a material opposite to ductility. It is
the property of breaking of a material with little
permanent distortion. Brittle materials when subjected to
tensile loads, snap off without giving any sensible
elongation. Cast iron is a brittle material.
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Testing Type
Destructive Testing
Hardness Testing
Brinell Test
Vickers Test
Rockwell Test
Shore Test
Impact Testing
Izod Test
Charpy Test
Non-Destructive
Testing
Penetration Test
Magnet Powder Test
Ultrasound Test
X-ray Test
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DESTRUCTIVE TESTING
HARDNESS TESTING
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Hardness testing
The Brinell hardness test method consists of indenting
(lekuk) the test material with a 10 mm diameter
hardened steel or carbide ball subjected to a load of
3000 kg.
For softer materials the load can be reduced to 1500
kg or 500 kg to avoid excessive indentation.
The full load is normally applied for 10 to 15 seconds in
the case of iron and steel and for at least 30 seconds in
the case of other metals.
The diameter of the indentation left in the test material
is measured with a low powered microscope.
The Brinell harness number is calculated by dividing the
load applied by the surface area of the indentation. 11
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Hardness testing formula
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BRINELL TESTING
The indenter is
pressed into the
metal
Softer materials
leave a deeper
indentation
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Brinell Test
Uses ball shaped indentor.
Cannot be used for thin
materials.
Ball may deform on very hard
materials
Surface area of indentation is
measured.
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Hardness testing machine
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Exercise
Brinell testing uses a metal ball with 10 mm diameter
size and the material used is aluminium alloy(K=5). As
a result, the value of dent diameter is 2.5 mm.
Calculate the load used and Brinell hardness value.
Solution
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Vickers Testing
The Vickers hardness test method consists of indenting the
test material with a diamond indenter, in the form of a right
pyramid with a square base and an angle of 136 degrees
between opposite faces subjected to a load of 1 to 100 kg.
The full load is normally applied for 10 to 15 seconds.
The two diagonals of the indentation left in the surface of
the material after removal of the load are measured using a
microscope and their average calculated.
The area of the sloping surface of the indentation is
calculated.
The Vickers hardness is the quotient obtained by dividing
the kg load by the square mm area of indentation.
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Vickers testing formula
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Vickers hardness test
Uses square shaped pyramid
indentor.
Accurate results.
Measures length of diagonal
on indentation.
Usually used on very hard
materials
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Exercise
A metal with 50 kg load is tested in Vickers testing. As a
result, the value of min distance between the sharp
diagonal is 0.432 mm. Calculate the Vickers hardness
value.
Solution:
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Rockwell hardness tests
Gives direct reading.
Rockwell B (ball) used for soft materials.
Rockwell C (cone) uses diamond cone for hard
materials.
Rockwell hardness number (HR)
HR= E - e
E = a constant depending on form of indenter
e = permanent increase in depth of
penetration due to major load F1 measured in
units of
Flexible, quick and easy to use.
Below figure show Rockwell principle
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Shore Scleroscope Testing
The Scleroscope test consists of dropping
a diamond tipped hammer, which falls
inside a glass tube under the force of its
own weight from a fixed height, onto the
test specimen.
The height of the rebound travel of the
hammer is measured on a graduated
scale.
The harder the material, the higher the
rebound.
The shore scleroscope test does not
normally mark the material under test.
The Shore Scleroscope measures
hardness in relation to the elasticity of
the material.
Advantages of this method are portability
and non-marking of the test surface.
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DESTRUCTIVE TESTING
IMPACT TEST
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Izod test
Izod specimen is a cantilever
beam with a notch on the
tension side to ensure
fracture when the impact load
is applied
Test specimen is held
vertically.
Strikes at 167 Joules.
Notch faces striker.
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Charpy impact test
Strikes form higher
position with 300 Joules.
Test specimen is held
horizontally.
Notch faces away from
striker.
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Impact Fracture
Brittle Fracture Ductile Fracture
If the material breaks on a
flat plane, the fracture was
brittle
If the material breaks with
jagged edges or shear lips,
then the fracture was
ductile.
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Impact Fracture
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Factors affecting Impact properties
If the dimensions of the specimen are increased, the
impact strength also increases.
When the sharpness of the notch increase, the impact
strength required causing failure decreases.
The temperature of the specimen under test gives an
indication about the type of fractures like ductile, brittle
or ductile to brittle transition.
The angle of the notch also improves impact-strength
after certain values.
The velocity of impact also affects impact strength to
some extent.
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NON-DESTRUCTIVE TESTING
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Non-Destructive Testing (NDT)
Non-Destructive – testing does not affect the structural
integrity of the sample. Samples or finished articles are
tested before being used. ( A measurement that does
not effect the specimen in any way) e.g., liquid
penetration, x-ray, etc.
NDT - general name for all methods which permit
testing / inspection of materials / parts without
impairing its future usefulness
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Types of defects
inherent defects - present during initial production of
raw materials
processing defects - resulted from the manufacturing
process
service defects - occurred during the operation
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Examples of causes of defects
Blowholes - gas trapped during solidification process
Segregation - during solidification of alloy
Scale - oxide formation on the surface of a metal heated to high
temperature
Stress - residual stress after cold working or rapid cooling
quenching / hardening cracks - rapid volume change
tempering cracks - rapid heating
shrinkage cracks - rapid cooling
grinding cracks - friction heating
also caused by residual stress, collapsed blowholes, improper rolling, sharp edge of
dies etc. etc.
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Penetrant testing
Used for surface flaws (imperfection/kecacatan).
The oil and chalk test is a traditional version of this type
of testing.
Coloured dyes are now used.
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Penetrant testing-application
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Magnetic particle testing
• Used for ferrous metals.
• Detects flaws close to the surface of the material.
• The component to be tested must first be magnetized.
• Magnetic particles which can be dry or in solution are sprinkled(ditaburkan) onto the test piece.
• The particles stick to the magnetic field and flaws can be inspected visually by examining the pattern to see if it has been distorted.
• The component must be demagnetized after testing.
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Magnetic particle testing-application
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Example of fluorescent magnetic particle
inspection using UV light, with indications
highlighted.
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Ultrasonic testing
Ultrasonic Sound waves are bounced off the component and back to a receiver. If there is a change in the time taken for the wave to return this will show a flaw.
Operation.
1. The ultrasonic probe sends the sound wave through the piece.
2. The sound wave bounces off the piece and returns.
3. The results are then placed on the display screen in the form of peaks.
4. Where the peaks fluctuate this will show a fault in the piece.
Uses.
This is generally used to find internal flaws in large forgings, castings and in weld inspections.
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Ultrasound testing-application
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Radiography (X-ray) Testing
1. The x-ray are released by heating the cathode.
2. They are then accelerated by the D.C. current and directed onto the piece by the tungsten anode.
3. The x-rays then pass through the test piece onto an x-ray film which displays the results.
4. The x-rays cannot pass through the faults as easily making them visible on the x-ray film.
Uses.
This is a test generally used to find internal flaws in materials. It is used to check the quality of welds, for example, to find voids or cracks.
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Radiography (X-ray) Testing-application
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Quiz time
Which of the following is a destructive
test ? A: magnet particle
B: rockwell testing
C: die penetrate testing
D: ultrasonic testing
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Quiz time
Ductility is the ability of a metal to ________ before
it breaks.
A: Bend
B: Stretch or elongate
C: Be forged
D: Be indented
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Quiz time
A Charpy test measures a welds ability to withstand
_________ force.
A: Impact
B: Bending
C: Penetrating
D: Stretching
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Quiz time
Hardness may be defined as the resistance to
__________?
Indentation