Chapter 1 of 10All chapters
Chapter 1 of 10
Describing a material
The vocabulary that matters.
The main properties
Strength is the load before failure. Stiffness resists deformation. Toughness absorbs energy before fracture. Hardness resists scratching. They are independent and often traded against each other.
- Glass is stiff, hard and not tough: it shatters.
- Rubber is tough and not stiff: it stretches enormously and returns.
Stress and strain
Stress is force per unit area and strain is proportional deformation. Plotting one against the other gives a curve that describes almost everything about how a material behaves.