Mechanical Properties of Solids

Strain is dimensionless, Strain has units of m/m, Strain = Change in dimension/Original dimension, Strain is a ratio of similar quantities

Strain is the ratio of change in dimension to original dimension. Since both quantities have the same units (length), strain is dimensionless. It's a geometric property independent of material type.

Change in length

Young's modulus (Y) is the ratio of longitudinal stress to longitudinal strain. It measures the resistance of a material to change in length under tensile or compressive forces.

Tensile stress, Compressive stress, Shearing stress, Volume stress

The three main types of stress are: 1) Tensile/Compressive stress (change in length), 2) Volume/Hydraulic stress (change in volume), and 3) Shearing stress (change in shape). Linear stress is not a standard classification.

Bulk modulus

Bulk modulus (K) is the ratio of volume stress to volume strain. It measures the resistance of a material to uniform compression from all sides, causing change in volume.