Materials and Their Properties
Categories and properties
Know the main families: hardwoods (oak, ash, mahogany), softwoods (pine, spruce), manufactured boards (plywood, MDF, chipboard), ferrous metals (steel, cast iron), non-ferrous metals (aluminium, copper, brass), thermoplastics (acrylic, HDPE, polystyrene), thermosetting plastics (epoxy, melamine) and composites (GRP, carbon fibre). For each, understand density, strength, hardness, toughness, elasticity, malleability, ductility, conductivity and resistance to corrosion.
Selection and stock forms
Materials are selected against the specification. Metals come as sheet, rod, tube and bar; timber as plank, board and moulding; plastics as sheet, rod and granules. Grain direction in timber and rolling direction in metal affect strength and bending, a frequent exam trap.
Testing and treatment
Know simple tests: the scratch test for hardness, the bend test for toughness, and the file test to distinguish ferrous from non-ferrous metals (ferrous filings attract a magnet). Understand heat treatment of steel: annealing softens, hardening and tempering trade hardness against brittleness. Know why timber is seasoned and why metals are galvanised or anodised.
Worked example: choosing a material
For a child's outdoor climbing frame you need strength, weather resistance and low maintenance. Mild steel would rust unless galvanised or painted; timber needs preservative treatment; aluminium is light and corrosion-resistant but weaker and more expensive. A galvanised steel frame with plastic end caps is a defensible answer, provided you justify each property against the specification.
Rule of thumb
Never name a material without naming the property that makes it suitable, and the property that is a drawback.