Mechanical Properties of Solids
1. Interatomic Forces in Solids
- Atoms in solids are held by strong intermolecular forces.
- Solids resist changes in shape and volume due to these forces.
2. Stress
- Force applied per unit area on a body.
- Formula: Stress = Force / Area
- Unit: N/m² or Pascal (Pa)
- Types: Longitudinal, Shearing, and Hydraulic stress
3. Strain
- Deformation produced in the body due to stress.
- Strain = Change in dimension / Original dimension
- It is a dimensionless quantity (no units).
4. Hooke’s Law
- Within elastic limits, stress is directly proportional to strain.
- Stress ∝ Strain ⇒ Stress = E × Strain
- E is the modulus of elasticity.
5. Types of Moduli of Elasticity
- Young’s Modulus (Y): Ratio of longitudinal stress to longitudinal strain.
- Shear Modulus (η): Ratio of shear stress to shear strain.
- Bulk Modulus (K): Ratio of hydraulic stress to the corresponding strain.
6. Stress-Strain Curve
- Graph showing the relation between stress and strain.
- Elastic limit is the point up to which Hooke’s Law is obeyed.
- Beyond the elastic limit, the material shows plastic behavior.
- Ultimate tensile strength: maximum stress the material can bear.
- Breaking point: point at which the material breaks.
7. Elastic and Plastic Behavior
- Elastic: regains original shape after stress is removed.
- Plastic: permanent deformation even after stress is removed.
8. Breaking Stress
- Maximum stress a material can handle before breaking.
- Depends on material type and temperature.