Chapter Four Week 10

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Diploma in Mechanical Engineering (Material)

JF 302 MATERIAL TECHNOLOGY 1

www.pis.edu.my

peneraju ilmu sejagat

Week 10


CLO 3 : Show various principles of materials testing

and material defects.


Describe materials testing

Define mechanical properties

Describe destructive tests

Describe non destructive tests


materials testing mechanical properties destructive tests non destructive tests

Hardness is the ability to withstand dents or scratches.

HARDNESS



Think critically 4.8

Why are the top 10 strongest

materials on Earth?




Why are the top 10 strongest

materials on Earth?

Wurtzite Boron Nitride

from valcanic residue

Lonsdaleite from

meteoroids

Diamond Borazon (boron +

nitrogen)

Synthetic Rhenium

Diboride

Titanium Carbide

(ceramic materials)

Titanium Diboride Zirconium Carbide Boron Carbide Alumina/ Aluminium

Oxide

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HARDNESS TESTING

MACHINE

The indenter is pressed into the metal

Softer materials leave a deeper indentation

Hardness Test methods : Brinell Test

Vickers Test

Rockwell Test

Knoop Test

Shore Test




Match the following indenters:-

Knoop

Brinell

Vickers

Rockwell




Match the following indenters:-

Knoop

Brinell

Vickers

Rockwell



BRINELL HARDNESS

TEST

Hardness is measured by pressing a hard steel ball into the surface of the test piece

using a known load.

A steel ball indenter of (10, 5, 1mm) diameter, indent into the surface of a metal with

fixed load of 500kg (4.905kN), 1500kg (14.715kN) or 3000kg (29.43kN) and

remained for 10 to 15 seconds.

Combination of load (P) and ball size (D) must be accurate to avoid distortion.

P = K where K is constant

D2



BRINELL HARDNESS

TEST

P = K where K is constant

D2

Typical K values are:-



BRINELL HARDNESS

TEST

Surface area of indentation with diameter d (mm) indented by ball indenter D (mm)

is given by the following formula :

Area = D [ D - (D2 d2)] mm2 2

Brinell Hardness Number (HB) given by :

HB = test load

surface area of indentation

= 2 P

D [ D - (D2 d2) ]

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VICKERS HARDNESS

TEST

Diamond pyramid (6000 HB) test indentor with an angle of 136, gives an indentation

that appears as a square. Indented with static loads for 10 to 15 minutes.

Static loads applied for materials used :

Materials Loads (kgf)

Steel and cast iron 30

Cuprum alloys 10

Pure cuprum, aluminium alloys 5

Pure aluminium 2.5

Lead (PB), tin (St) and tin alloys 1



VICKERS HARDNESS

TEST

The Vickers Hardness Number (HV) given by the formula below :

HV = Test loads

Surface area of the indentation

= F (kgf)

d2 / [2 sin / 2] where = 136

= 2 F sin 68

d2

= 1.8544 F

d2

F = test load (kg)

d = average length of diagonals (mm)




Indicate the HV value for a steel with

d1= 183m and d2=209m.




Indicate the HV value for a steel with

d1= 183m and d2=209m.

HV = 1.8544 F

d2

= 1.8544 (30)

(196 x 10-3)2

= 1448HV/30

d = d1 + d2

2

= 183 + 209

2

= 196m

= 196 x 10-3 mm



ROCKWELL HARDNESS

TEST

(a) Unloaded

(b) Minor load applied

(c) Major load applied

(d) Loads were released

d - the differentiate of indentation depth by P1 and P2



ROCKWELL HARDNESS

TEST

The indenters most commonly used are :

1. diamond cone with an apex angle of 120

2. hard steel ball by varies of diameter

Scale Indenter Loads

First Major Total

B (ball) Hard steel ball 1.6mm 10 90 100

C (cone) Diamond cone with apex angle of 120 10 140 150

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ROCKWELL HARDNESS

TEST

Scale Indenter Loads

First Major Total

B (ball) Hard steel ball 1.6mm 10 90 100

C (cone) Diamond cone with apex angle of 120 10 140 150



KNOOP HARDNESS

TEST

Principle :

To determine the hardness over very small areas or the hardness of certain micro-

constituents for identification purposes.

Requires the use of extremely low loads, careful surface preparation of the specimen

and measurement of indentation at higher magnification.



KNOOP HARDNESS

TEST

Knoop indenter is a diamond ground to a pyramidal form that produces a diamond-

shaped indentation with the long and short diagonals by using 25g to 5kg of loads.

It is suitable to test smaller and thinner specimen, brittle material such as gem stones,

carbide and glass, and to measure grain hardness in metal.

The indenter size is between 0.01 to 0.1mm, the length of the indent is seven times

longer than its width and almost 30 times bigger than its depth.



KNOOP HARDNESS

TEST

The Knoop Hardness Number (HK) given as the formula below :

HK = Test load (kgf)

Area of spread indentation (mm2)

= P

CPL2 L = length of indentation along its long axis

Cp = correction factor related to the shape of the

= indenter, ideally 0.070279

P = load



KNOOP HARDNESS

TEST

The advantages of the test are that only a very

small sample of material is required, and that it is

valid for a wide range of test forces.

The main disadvantages are the difficulty of using a

microscope to measure the indentation (with an

accuracy of 0.5 micrometre), and the time needed to

prepare the sample and apply the indenter.



SHORE HARDNESS

TEST

Durometer is the hardness tester for shore hardness test of a material.

It measures the depth of an indentation in the material created by a given force on a

standardized presser foot.

This depth is dependent on the hardness of the material, its visco-elastic properties,

the shape of the presser foot, and the duration of the test.

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SHORE HARDNESS

TEST

Method of measurement:

The basic test requires applying the force in a consistent manner, without shock, and

measuring the hardness (depth of the indentation).

If a timed hardness is desired, force is applied for the required time and then read.

The material under test should be a minimum of 6.4 mm (0.25 inches) thick.



Impact is the force or energy of a collision of two objects.

Toughness is a measurement of the amount of energy a

material can absorb before fracturing.

IMPACT



IMPACT TEST

Principle :

Striking a specimen with a controlled

pendulum and measuring the energy

absorbed in bending or breaking the

specimen.

The energy value indicates the

toughness of the material.




Match the correct type of impact test.

Izod

Charpy




Match the correct type of impact test.

Izod

Charpy



IZOD IMPACT TEST

1. Breaking by one blow from a

swinging hammer (with 162J of the

kinetic energy and 3.8m/s of

velocity).

2. A test piece gripped vertically at the

bottom.

3. The notch in the same plane as the

upper face of the grips.

4. The blow is struck at a fixed

position facing the notch.

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CHARPY IMPACT TEST

1. Breaking by one blow from a

swinging hammer (with 300J of the

kinetic energy and 5m/s of velocity).

2. The test piece is notched in the

middle.

3. The test piece is supported at each

end as a beam.

4. The test piece should be in

horizontal position, struck by the

hammer in the plane of symmetry of

the notch.



It can be seen that at low temperatures the material is more brittle and

impact toughness is low. At high temperatures the material is more ductile

and impact toughness is higher.

The transition temperature is the boundary between brittle and ductile

behaviour.

Effect of temperature to

impact toughness



Tensile indicates how the material will react to forces being

applied in tension.

A tensile test is a fundamental mechanical test where a

carefully prepared specimen is loaded in a controlled manner

while measuring the applied load and the elongation of the

specimen over some distance.

TENSILE




What are the properties that a tensile

test can determine?

Hardness

Tensile strength Elastic limit

Yield strength

Modulus of elastic

Fracture Reduction in area

Elongation




What are the properties that a tensile

test can determine?

Hardness

Tensile strength Yield strength

Modulus of elastic

Fracture Elongation

Elastic limit

Reduction in area



TENSILE TEST

SPECIMENS

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STRESS-STRAIN

GRAPH

tens

ile s

tren

gth

uppe

r yi

eld

poin

t

Pro

port

iona

lity

rang

e

Lo

ad f

or

forc

e kN

Elastic

limit

Limit of proportionality

The extension of a metal

is proportional to the

force up to the limit of

proportionality

Returns to original length

Gauge

length

Necking

Gauge

length

Gauge

length

Cup and Cone

Low

er y

ield

poi

nt

Strain

Stress



STRESS-STRAIN

GRAPH

The stress and strain initially increase with a linear

relationship (with no plastic deformation).

In this region of the curve, when the stress is

reduced, the material will return to its original shape

(elastic deformation).

The slope of the line in this region where stress is

proportional to strain and is called the modulus of elasticity or Young's modulus.



STRESS-STRAIN

GRAPH

Increasing of stress or load leads to some permanent

deformation in the specimen and the material is deformed

plastically.

The material will not return to its original condition when

the load is removed.

The yield strength is defined as the stress required to

produce a small, amount of plastic deformation.

Lower yield point is the minimum stress required to

produce plastic deformation.



STRESS-STRAIN

GRAPH

The ultimate tensile strength (UTS) or

the tensile strength, is the maximum

engineering stress level reached in a

tension test.

The strength of a material is its ability

to withstand external forces without

breaking in necking phenomena.



STRESS-STRAIN

GRAPH

Fracture cup and cone of a

material.




Draw a stress-strain graph for this

tensile test.

The following data was obtained from a tensile test on a specimen of 10mm diameter and

gauge length 60mm.

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Draw a stress-strain graph for this

tensile test.


Describe creep and fatigue?


Chapter Four Week 10

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