Mechanical properties of a materials
➤ Elasticity:
→ Elasticity of a material
is its power of coming back to its original position after deformation when the
stress or load is removed.
→ Elasticity is a tensile property of its material.
➤ Stiffness:
→ It is the property of a material due to which it is capable
of resisting deflection or elastic deformation under applied loads. also called
rigidity.
→ The degree of stiffness of a material is indicated by the young’s
modulus.
→ The steel beam is stiffer or more rigid than aluminum beam.
➤ Plasticity:
→ The plasticity of a material is its ability to change some degree
of permanent deformation without failure.
→ This property is widely used in
several mechanical processes like forming, shaping, extruding, rolling etc.
→ Due
to this properties various metal can be transformed into different products of
required shape and size.
→ This conversion into desired shape and size is
effected either by the application of pressure , heat or both.
→ Plasticity
increase with increase in temp.
➤ Malleability:
→ Malleability of a material is its ability to be flattened
into their sheets without creaking by hot or cold working.
→ Aluminum, copper,
tin lead steel etc. are malleable metals.
➤ Ductility:
→ Ductility is that property of a material, which enables it to
draw out into thin wire.
→ Mild steel is a ductile material.
→ The percent
elongation and the reduction in area in tension is often used as empirical
measures of ductility.
➤ Brittleness:
→ The brittleness of a material is the property of breaking
without much permanent distortion.
→ There are many materials, which break or
fail before much deformation take place. Such materials are brittle e.g. glass,
cast iron.
→ Therefore a non-ductile material is said to be a brittle material.
→ Usually the tensile strength of brittle materials is only a fraction of their
compressive strength.
→ A brittle material should not be considered as lacking in
strength. It only shows the lack of plasticity.
➤ Toughness:
→ Toughness is a measure of the amount of energy a material can
absorb before actual fracture or failure takes place.
→ The toughness of a
material is its ability to withstand both plastic and elastic deformation.
→ The
work or energy a material absorbs is called modulus of toughness.
→ For Examples: If a load is
suddenly applied to a piece of mild steel and then to a piece of glass the mild
steel will absorb much more energy before failure occurs.
→ Thus mild steel is
said to be much tougher than a glass.
➤ Hardness:
→ Hardness is defined in
terms of the ability of a material to resist screeching, abrasion, cutting,
indentation or penetration.
→ Many methods are now in use for determining the
hardness of a material. They are Brinell, Rockwell and Vickers.
→ Hardness of a metal does not directly related to the hardenability of the metal.
→ Hardenability is indicative of the degree of hardness that the metal can
acquire through the hardening process. i.e., heating or quenching.
➤ Impact Strength:
→ It can be defined as the resistance of the material to
fracture under impact loading, i.e under quickly applied dynamic loads.
→ Two
standard tests are normally used to determine this property.
➤ Fatigue :
→ Failure of a material
under repeated stress is known as fatigue and the maximum stress that a metal
can withstand without failure for a specific large number of cycle of stress is
called Fatigue limit.
➤ Creep:
→ The slow and progressive deformation of a material with time at constant
stress is called creep.
→ There are three stages of creep.
→ In the first one, the
material elongates rapidly but at a decreasing rate.
→ In the second stage, the
rate of elongation is constant.
→ In the third stage, the rate of elongation
increases rapidly until the material fails.
→ The stress for a specified rate of
strain at a constant temperature is called creep strength.
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