chapter four week 10
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aTRANSCRIPT
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4/9/2014
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Diploma in Mechanical Engineering (Material)
JF 302 MATERIAL TECHNOLOGY 1
www.pis.edu.my
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Week 10
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CLO 3 : Show various principles of materials testing
and material defects.
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Describe materials testing
Define mechanical properties
Describe destructive tests
Describe non destructive tests
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Hardness is the ability to withstand dents or scratches.
HARDNESS
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Think critically 4.8
Why are the top 10 strongest
materials on Earth?
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Think critically 4.8
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
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Think critically 4.9
Match the following indenters:-
Knoop
Brinell
Vickers
Rockwell
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Think critically 4.9
Match the following indenters:-
Knoop
Brinell
Vickers
Rockwell
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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
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BRINELL HARDNESS
TEST
P = K where K is constant
D2
Typical K values are:-
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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
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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)
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Think critically 4.10
Indicate the HV value for a steel with
d1= 183m and d2=209m.
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Think critically 4.10
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
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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
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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
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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.
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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.
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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
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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.
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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.
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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
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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.
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Think critically 4.11
Match the correct type of impact test.
Izod
Charpy
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Think critically 4.11
Match the correct type of impact test.
Izod
Charpy
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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.
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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
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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
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Think critically 4.12
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
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Think critically 4.12
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
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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
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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.
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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.
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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.
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STRESS-STRAIN
GRAPH
Fracture cup and cone of a
material.
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Think critically 4.13
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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Think critically 4.13
Draw a stress-strain graph for this
tensile test.
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Describe creep and fatigue?
materials testing mechanical properties destructive tests non destructive tests