Materials and their properties
What the domain tests
Materials and their properties tests selection, not memorised lists. You need to distinguish ferrous and non-ferrous metals, alloys, thermoplastics and thermosets, natural and manufactured timber, and composites, then justify a material from service conditions. Expect questions on strength, hardness, toughness, ductility, malleability, elasticity, thermal and electrical conductivity, density, and corrosion.
Core rules and concepts
- Ferrous metals contain iron and are magnetic; most rust unless protected. Non-ferrous metals include aluminium, copper and zinc. Alloys are mixtures, such as brass (copper and zinc) and stainless steel (iron, chromium and often nickel).
- Thermoplastics soften on heating and can be reshaped; thermosets cure permanently and char rather than melt. This affects recycling and heat resistance.
- Hardwoods come from broad-leaved trees and softwoods from conifers; the terms do not simply mean hard and soft. Grain direction affects strength and how timber splits.
- Manufactured boards such as plywood and MDF use adhesives and have more uniform properties than solid timber, but edges and moisture resistance need attention.
- A composite combines materials to gain properties neither has alone; glass-reinforced plastic is strong and light but difficult to recycle.
Worked example
An outdoor bracket must carry a 15 kg load, resist rain and stay within a school budget. Mild steel is strong and cheap but corrodes, so it would need galvanising or painting. Aluminium is light and corrosion-resistant but more flexible and costly. Stainless steel resists corrosion and is strong but expensive and harder to cut. Galvanised mild steel is the justified compromise if the coating is not damaged during drilling; the answer should state that exposed cut edges need protection.
Traps that cost marks
Do not use “strong” for every property. Hardness is not toughness, and stiffness is not strength. Do not assume all stainless steel is magnetic, or that all plastics are recyclable. Ignoring the service environment loses selection marks.