🧱 Mechanical Properties of Solids

1. Elasticity and Plasticity

Elasticity is the property of a body by virtue of which it regains its original shape and size after the deforming force is removed.

Plasticity is the property where a body does not regain its original shape at all (e.g., putty or mud).

The restoring force per unit area. Stress = F / A. Unit: N/m² or Pascal (Pa).

Types: Longitudinal (tensile/compressive), Tangential (Shear), and Hydraulic (Volume) stress.

The fractional change in dimension. Strain = Change in dimension / Original dimension. It has no units.

Within the elastic limit, stress is directly proportional to strain.

Stress ∝ Strain ⇒ Stress = E × Strain Where E is the Modulus of Elasticity.

Young's Modulus (Y): Longitudinal Stress / Longitudinal Strain. (Applicable to solids).
Shear Modulus or Rigidity Modulus (G): Shear Stress / Shear Strain.
Bulk Modulus (B): Hydraulic Stress / Volumetric Strain. (Applicable to solids, liquids, and gases). The reciprocal of Bulk Modulus is Compressibility.

When a wire is stretched, work is done against interatomic forces. This work is stored as elastic potential energy.

U = ½ × Stress × Strain × Volume