2. INTRODUCTION
The practical application of engineering materials
in manufacturing engineering depends upon
through knowledge of their particular properties
under wide range of conditions.
The term “property” is a qualitative or
quantitative measure of response of materials to
externally imposed conditions like forces and
temperature.
However, the range of properties found in
different classes of materials is very large.
3. CLASSIFICATION OF MATERIAL PROPERTY:
Materials properties
Mechanical
thermal
opitcal
physical
magnetic
chemical
technological
electrical
4. MECHANICAL PROPERTIES:
The properties of materials that determines its
behaviour under applied forces are called
mechanical properties.
They are usually related to the elastic and plastic
behaviour of the material.
These properties are expressed as the function of
stress-strain.etc
A sound knowledge of mechanical properties of
materials provides the basis for predicting
behaviour of materials under different load
conditions and designing the components out of
them.
6. STRESS -STRAIN
Experience shows that any materials subjected to a load
may either deform , yield or break , depending upon-
The magnitude of load
Nature of the material
Cross sectional dimension
The engineering stress and strain are based on the
original sample dimension which changes during test.
True stress and strain on other hand based on actual or
instantaneous dimensions and are better representation
of deformation behaviour of the material.
7. Engineering stress and strain curve is based on original area ,it
descends after maximum load as the load bearing capacity of
sample decrease due to reduction in area.
True stress-strain curve, continue to go up till fracture as it is based
on actual area
Engineering stress – strain curve
True stress-strain
curve
8. ELASTICITY
The property of material by virtue of which deformation
caused by applied loads disappears upon removal of load.
Elasticity of the material is the power of coming back to its
original position after deformation when the stress or load is
removed.
9. The physical reasons for elastic behavior can be quite
different for different materials. In metals, the atomic
lattice changes size and shape when forces are applied
(energy is added to the system). When forces are
removed, the lattice goes back to the original lower
energy state.
In engineering, the amount of elasticity of a material is
determined by two types of material parameter.
The first type of material parameter is called a modulus,
which measures the amount of force per unit area (stress)
needed to achieve a given amount of deformation. The
units of modulus are pascals (Pa).
A higher modulus typically indicates that the material is
harder to deform.
10. The second type of parameter measures the elastic limit.
The limit can be a stress beyond which the material no
longer behaves elastic and deformation of the material
will take place.
If the stress is released, the material will elastically
return to a permanent deformed shape instead of the
original shape.
11. PLASTICITY:
The plasticity of a material is its ability to undergo some
degree of permanent deformation without rupture or
failure.
Plastic deformation will take only after the elastic limit is
exceeded.
It increases with increase in temperature.
13. DUCTILITY:
It is the ability of a material to undergo plastic
deformation without fracture.
Ex:- Mild steel is ductile material.
14. There are two common measure of ductility:-
1). Percentage elongation:-% elongation describes the extent
to which specimen structure before repture.
% elongation=Lf-Lo/Lo*100
where, Lf= final gauge length
Lo = initial gauge length
15. 2). Percentage reduction:- % reduction is a measure %
change in cross sectional area at point of fracture before and
after the test.
% reduction=Af-Ao/Ao*100
where,
Af= final cross sectional area
Ao= initial cross sectional area
16. The amount of ductility is an important factor when considering
forming operations such as rolling and extrusion. Ductility is
also used a quality control measure to assess the level of
impurities and proper processing of a material.
For ductile material, breaking strength is less than UTS ,and
necking precedes fracture.
For brittle material, fracture usually occur before necking and
possibly before the onset of plastic flow.
17. TOUGHNESS
Toughness is the ability of the material to absorb energy
during plastic deformation upto fracture.
.A material with high strength and high ductility will have
more toughness than a material with low strength and high
ductility.
Toughness is a good combination of strength and ductility.
one way to measure toughness is by calculating the area
under the stress strain curve from a tensile test. This value is
simply called “material toughness” and it has units of energy
per volume.
Material toughness equates to a slow absorption of energy
by the material.
18. several variables that have a profound influence on the toughness of
a material:-
1). Strain rate - metal may possess satisfactory toughness under
static loads but may fail under dynamic loads or impact. toughness
decrease as the rate of loading increases.
19. 2). Temperature:- Temperature is the second variable to
have a major influence on its toughness. As temperature is
lowered, the ductility and toughness also decrease.
3). Notch effect:- The third variable is termed notch effect,
has to due with the distribution of stress. A material might
display good toughness when the applied stress is uniaxial.
Two of the toughness properties that will be discussed in
more detail are:-
1).Impact toughness- The impact toughness of a material can
be determined with a Charpy test.
Impact tests continue to be used as a quality control method
to assess notch sensitivity and for comparing the relative
toughness of engineering materials.
20. Toughness is greatly affected by temperature, a Charpy test is
often repeated numerous times with each specimen tested at a
different temperature.
FIG-CHARPY TESTER
21. This produces a graph of impact toughness for the material as a
function of temperature.
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 behavior and this temperature is often an extremely
important consideration in the selection of a material.
22. 2). Notch-Toughness:
Notch toughness is the ability that a material possesses to
absorb energy in the presence of a flaw.
Notch-toughness is measured with a variety of specimens such
as the Charpy V-notch impact specimen or the dynamic tear
test specimen.
impact testing the tests are often repeated numerous times
with specimens tested at a different temperature.
With these specimens and by varying the loading speed and
the temperature, it is possible to generate curves such as those
shown in the graph.
The material develops plastic strains as the yield stress is
exceeded in the region near the crack tip.
23. The amount of plastic deformation is restricted by the
surrounding material, which remains elastic.When a material is
prevented from deforming plastically, it fails in a brittle
manner.
24. It is the property of a metal, which gives it the
ability to resist being permanently deformed
when a load is applied.
The greater the hardness of the metal, the
greater resistance against the deformation.
25. Various hardening process
Hall- Petch strengthening (Grain boundary)
Work hardening
Solid solution strengthening
Precipitation hardening
Martensitic transformation
26. MEASUREMENT METHODS
Rockwell hardness test
Brinell hardness test
Vickers hardness test
Knoop hardness
Shore
Mohs test
Barcol hardness test
29. FATIGUE
Metal fatigue is the progressive and localized
structural damage that occurs when a material is
subjected to cyclic loadings.
The highest stress that a material can withstand
for an infinite number of cycles without breaking
called also endurance limit
The greater the applied stress range, the shorter
the life.
30.
31. Prediction of fatigue
1)S-N Curve
2)Strain life relationship
3)Fracture mechanics approach
4) Goodman life equation
34. CREEP
The tendency of a solid material to deform
permanently under the influence of
mechanical stresses.
It can occur as a result of long-term exposure to
high levels of stress that are still below the yield
strength of the material.
Creep is more severe in materials that are
subjected to heat for long periods, and generally
increases as they near their melting point.
38. WEAR
Wear is related to interactions between surfaces and
specifically the removal and deformation of material
on a surface as a result of mechanical action of the
opposite surface.
40. Measurement of wear
Tribometer Archard equation
Q=KWL/H
where
Q is the total volume of wear
debris produced
K is a dimensionless constant
W is the total normal load
L is the sliding distance
H is the hardness of the softest
contacting surfaces
Note that is proportional to the
work done by the friction forces
as described by Reye's
hypothesis.
