Materials, Components and their Properties
This domain tests material selection: matching properties, stock forms, cost and processing to a product's function. Questions ask you to define properties, compare material families, choose standard components, and justify a choice using service conditions rather than brand names.
Core concepts
- Mechanical properties: tensile, compressive and shear strength; stiffness; hardness (resistance to indentation); toughness (energy absorbed before fracture); ductility; malleability; elasticity.
- Physical properties: density, thermal and electrical conductivity, thermal expansion, melting point, corrosion resistance.
- Families: woods (hardwood and softwood), metals (ferrous and non-ferrous), polymers (thermoplastic and thermosetting), ceramics and composites.
- Stock forms: sheet, plate, bar, tube, rod, extruded section, moulding powder, yarn and weave.
- Standard components: screws, bolts, bearings, hinges, resistors, switches and connectors. They save design time and are replaceable.
Worked example
A pan handle needs low thermal conductivity, heat resistance above 150 °C, toughness and a secure grip. Solid stainless steel conducts heat to the hand and needs an insulated grip. Hardwood has low conductivity but chars and absorbs water. A phenolic resin handle resists heat but is brittle if dropped. A silicone sleeve over a steel insert combines a heat-resistant, high-friction grip with a strong fixing. Reasoning: no single property decides; the service conditions (heat, washing, impact, cost) set the priorities.
Traps
- Confusing hardness with toughness: glass is hard but not tough.
- Confusing strength with stiffness: a stiff material may still be weak.
- Choosing a material without considering stock form, joining method or available processing.
- Ignoring corrosion, UV exposure or food-contact requirements.