# Mechanical Properties of Materials

Mechanical properties helps us to measure how materials behave under a load. Mechanical properties of materials are mentioned below.

#### Elastic Material:

A material which regains its original size and shape on removal stress is said to be elastic stress.

#### Plastic material:

A material which can undergo permanent deformation without rupture aid to be plastic material. This property of the material is known as plasticity. Plasticity is important when a material is to be mechanically formed by causing the material to flow.

#### Ductile Material:

A material which an undergo considerable deformation without rupture is said to be ductile material. The major portion of deformation is plastic.

#### Brittle Material:

A material which ruptures with little or no plastic deformation is said to brittle materials.

#### Set of Permanent set:

The deformation or strain remaining in a body after removal of stress is known as permanent set. This is due to elastic property of material.

#### Elastic limit:

The greatest stress that a material can take without permanent set on the removal of stress is known as elastic limit.

#### Proportionality limit:

The greatest stress that a material can take without deviation from straight line between stress and strain is known as proportionality limit.

#### Endurance limit or Fatigue limit:

The greatest stress, applied infinite number of times, that a material can take without causing failure is known as endurance limit or fatigue limit.

#### Ultimate Strength:

The maximum stress material can take is known as ultimate strength. Ultimate strength is equal to maximum load divided by original area of cross section.

#### Modulus of Resilience:

The energy stored per unit volume at the elastic limit is known as modulus of resilience.

#### Modulus of Toughness:

The amount of work required per unit volume to cause failure, under static loading, is called modulus of toughness.

#### Modulus of Rupture:

The ultimate strength in flexure or torsion is known as modulus of rupture.

#### Strain hardening:

The increase in strength after plastic zone due to rearrangement of molecules in the material.

#### Proof stress:

The stress which is just sufficient to cause a permanent set(elongation) equal to a specified percentage of the original gauge length.

#### Elastic Strain:

Elastic strain is a dimensional change that occur in a material due to the application of loads and disappears completely on the removal of the loads.

#### Plastic Strain:

It is a dimensional change that occurs in a material due to application of the loads and does not disappear after the removal of the loads.

#### Ductility and malleability:

The plastic response of material to tensile force is known as ductility and plastic response to compression force is known as malleability. The elongation and reduction of area of test piece tested to failure in tension are generally taken as measures of ductility of material.

#### Creep:

The long term deflection due to sustained (constant) loads.

#### Factor of Safety:

Factor of safety is defined as follows
For Ductile materials,
F.O.S = yield stress / working stress
For Brittle materials,
F.O.S = ultimate stress / working stress

#### Margin of Safety:

Margin of safety = Factor of safety – 1