Mechanical Properties

Plasticity:

The property of a material, which does not regain its original position on the removal of external forces, is called plasticity.

Ductility:

It is the property of a material, which enables it to be drawn into wires without rupture.

Brittleness:

It is the property of a material, which enables it to fail by rupture due to some external force with little permanent deformation. E.g. cast iron.

Malleability:

It is the property of a material, which enables it to be flattened into thin sheets without cracking by pressing.

Strength:

It is the ability of a material to resist the external applied forces without breaking or yielding.

Stiffness:

It is the ability of a material to resist deformation under stress. The modulus of elasticity is the measure of stiffness.

Elasticity:

It is the property of a material to regain its original shape under deformation when external forces are

removed.

Toughness:

It is the property of a material to resist fracture due to high impact load like hammer blows. The toughness of material decreases when it is heated.

Machinability:

It is the property, which refers to a relative case with which a material can be cut. It may be noted that brass can be easily machined than steel.

Resilience:

It is the property of a material to absorb energy and to resist shock and impact loads. It is measured by the amount of energy absorbed per unit volume within elastic limit.

Creep:

When a point is subjected to a constant stress at higher temperature for a long period of time, it will undergo a slow and permanent deformation called creep. This property is considered in designing

I.C. Engines, boilers and turbines.

Fatigue:

When a material is subjected to repeated stresses, it fails at stresses below the yield point stresses. Such a type of failure of a material is known as fatigue. This property is considered in designing shafts, connecting rods, springs, gears etc.

Hardness:

It is the property of a metal and has a wide variety of meanings. It embraces many different properties such as resistance to wear, scratching, deformation, machinability etc. It also means that ability of a metal to cut another metal.

The hardness is usually expressed in numbers, which are dependent on the method of making the test.

i. Brinell hardness

ii. Rockwell hardness

iii. Vickers hardness (diamond pyramid)

iv. Shore scleroscope

Endurance limit:

It is the limit up to which a member can withstand the repeated stress when applied ten million cycles. This limiting stress is also called fatigue limit.

Difference between Hardness and Toughness

Hardness i. It is the property of the material to resist scratching, abrasion, indentation or penetration. ii. Hardness of a material is stated relative to the hardness of other material. iii. Important in shafts, bearing whichever is having relative motion.

Toughness i. Ability of a material to withstand both elastic and plastic deformation, shock and vibration. ii. Toughness is measured in terms of the energy a material can absorb before a actual failure takes place. iii. Important in structural members, machine parts which are subjected to shock and vibration. E.g. shafts, spring.