Elasticity: The tendency of a material to
regain its original dimensions (size and shape) upon the
removal of load or force. Eg. Steel is more elastic than
rubber. The ratio between tensile stress and tensile strain
or Compressive stress and compressive strain is called
young’s modulus of Elasticity.
Young’s Modulus of elasticity = E = Stress/Strain = σ / ε
of rigidity or shear modulus is the ratio of shear stress to
the shear strain.
Modulus of Rigidity or Shear Modulus = Shear stress/shear
or Volume modulus of elasticity is the ratio of normal
stress to the volumetric strain.
Modulus = Normal stress/Volumetric strain
tendency of a material to permanently deform when subjected
to external load beyond the elastic limit.
The ability of a material to absorb energy in plastic
deformation till the point of fracture is known as
toughness. Toughness is indicated by the total area under
the stress strain curve up to the fracture point. Eg. Copper
has higher toughness than Cast iron.
Modulus of toughness = ½ (Ultimate Tensile strength + Yield
strength) X (elongation strength) X elongation
ability of a material to absorb energy under elastic
deformation and to recover this energy upon removal of load
is termed as resilience. Resilience is indicated by the area
under the stress strain curve till the point of elastic
Modulus of Resilience = (Yield strength)2 / 2
Modulus of elasticity
ability of a material to resist plastic deformation and
represents the stress below which the deformation is
entirely elastic in nature. The magnitude of yield strength
for a metal is a measure of resistance to plastic
6. Tensile strength or Ultimate tensile strength:
is the ratio of maximum stress that a material can withstand
without being fractured to the original area of cross
section of the material. Ultimate tensile strength or
tensile strength is the highest point in a stress-strain
7. Impact strength:
Ability of material to resist or absorb energy before it
fractures during plastic deformation. It is closely
associated with toughness with the difference that toughness
takes into account both the strength and ductility of the
material. Ductile materials have higher impact strength than
brittle materials. Impact strength can be measured by two
methods. (a). Izod Test (b). Charpy test
ability of a material to be drawn into wire is known as
ductility. It is a tensile property and it is the
capacity of a material to undergo deformation without being
fractured. It cab be measured as the percent (%) elongation
or percent area reduction.
elongation = [(lf – l0) / l0]
reduction = [(A0 – Af) / A0]
is the length at the point of fracture
is the original length
is the original cross section area
is the cross sectional at the point of fracture
The ability of a material to be formed into sheets by
hammering or rolling is called malleability. It is a
compressive property. e.g. Gold is the most malleable metal.
It is the tendency of a material to crack when it is
subjected to deformation. It is opposite to ductility and
malleability. e.g. Cast iron is a brittle material.
It is a deformation of a material due to the constant load
for a long period of time. It is time and temperature
dependent property of material. It takes place in three
stages. i.e. primary, secondary and tertiary. a). First
stage of creep known as primary creep occurs at relatively
low temperature and the creep rate decreases with time. b).
Second stage of creep known as secondary creep in the range
of 0.4 to 0.7 Tm i.e. is the absolute melting
temperature is a period of constant creep rate and hence
referred to as steady state creep. It is the most important
part of the creep curve for engineering applications. c).
The third stage of creep known as tertiary creep occurs
beyond 0.7 Tm has an accelerated rate and results
in fracture of the material.
body is subjected to repeated and fluctuating load it tends
to develop a characteristic behavior under which failure
occurs which is referred to as fatigue.
resistance offered by a material to indentation is referred
to as hardness of that material. It is the property by
virtue of which it can resist abrasion, scratching and
penetration. Hardness can be measured by the following
Rockwell hardness test
Vicker’s hardness test.
It indicates the degree of hardness that can be imparted to
a material by the process of hardening. It deals with the
depth and distribution of hardness that can be induced in
that particular material which can be increased by addition
of alloying elements.
Wear is the unintentional removal of the material from the
surface of the body. Wear is of two types. 1). Abrasive wear
2). Adhesive wear. Wear resistance is the ability of a
metal to resist this unintentional removal.