Engineering Materials and Their Properties
Engineering Materials and Their Properties
The exam checks whether you can match material properties to service conditions: strength, hardness, toughness, ductility, malleability, elasticity, conductivity and corrosion resistance.
Core rules
- Ferrous metals contain iron; mild steel has roughly 0.15–0.3% carbon, is ductile, weldable and cheap. Increasing carbon raises hardness and tensile strength but lowers ductility and weldability.
- Stainless steel relies on chromium (about 18%) and nickel (about 8%) to form a passive oxide layer; it resists corrosion but can still suffer crevice attack.
- Non-ferrous examples: aluminium is light, conducts heat and electricity and forms a protective oxide; copper conducts well and is ductile; brass is a copper-zinc alloy with good machinability.
- Polymers are light and corrosion-resistant but creep and soften with heat; composites combine reinforcement and matrix for high stiffness-to-weight.
- Tests: tensile test gives yield strength, ultimate tensile strength and elongation; Brinell, Vickers and Rockwell measure hardness; Charpy and Izod measure impact toughness.
Worked example
A bench vice jaw must resist indentation and wear, so a hard, wear-resistant steel is chosen. The handle must absorb sudden loads without snapping, so toughness and ductility matter more than maximum hardness. Selecting the hardest steel for both would make the handle brittle and unsafe.
Traps
Confusing strength with hardness; calling a brittle material tough; ignoring corrosion or temperature; assuming low density always means low strength.