Chapter 8 — Mechanical Properties of Solids

Mechanical Properties of Solids covers stress, strain, elasticity, and Hooke's law — how materials deform under force and regain shape. Understanding these properties is essential for engineering design of buildings, bridges, and structural elements.

This chapter examines how solids deform when external forces are applied and how they restore to original shape. Key concepts include stress (restoring force per unit area), strain (fractional dimensional change), and three types: tensile/compressive, shearing, and hydraulic. Hooke's law states stress is proportional to strain within the elastic limit. Three elastic moduli characterize material behavior: Young's modulus (Y) for longitudinal deformation, shear modulus (G) for shape change, and bulk modulus (B) for volume compression. Real applications include crane rope design, bridge beam geometry, and mountain height limits based on rock elasticity.

1. 01Elasticity is the property by which bodies regain original shape/size when external force is removed; plasticity is permanent deformation
2. 02Stress = F/A (force per unit area, SI unit Pa); Strain = ΔL/L (dimensionless ratio of dimension change)
3. 03Hooke's law: stress = k × strain (valid for small deformations within elastic limit); three types—longitudinal, shearing, hydraulic
4. 04Young's modulus Y = (F/A)/(ΔL/L); metals have large Y values (steel > copper > aluminium); shear modulus G ≈ Y/3
5. 05Bulk modulus B relates pressure to volume change; solids least compressible, gases ~1 million times more compressible
6. 06Stress-strain curve shows elastic region (O-A, Hooke's law valid), yield point (B), plastic deformation (B-D), ultimate tensile strength (D), brittle vs ductile behavior