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

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

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

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

Quiz time

A Charpy test measures a welds ability to withstand

_________ force.

A: Impact

B: Bending

C: Penetrating

D: Stretching

Quiz time

Hardness may be defined as the resistance to

__________?

Indentation