Engineering Materials and Their Properties
Engineering Materials and Their Properties
This domain tests classification of metals, matching a material property to a service requirement, and reading a tensile or hardness test result.
Metals you must know
- Ferrous: grey cast iron (2–4 % carbon, brittle, strong in compression, good damping - machine beds); mild steel (0.15–0.30 % C, ductile, weldable - general fabrication); high-carbon steel (0.6–1.5 % C, hard - tools, springs); alloy steels with Cr, Ni, Mo for strength and wear resistance.
- Non-ferrous: aluminium (light, corrosion resistant, low strength), copper (electrical and thermal conductivity), brass (Cu–Zn, easily machined), bronze (Cu–Sn, bushes and bearings), white metal (bearing linings).
Properties in one line each
Elasticity returns to shape; plasticity does not; ductility allows drawing into wire; malleability allows hammering into sheet; toughness absorbs energy before fracture; brittleness fractures with almost no elongation; hardness resists indentation; machinability rates ease of cutting.
Worked example
A 12.5 mm diameter mild-steel specimen of gauge length 50 mm breaks at 40 kN; the broken gauge length measures 62 mm. Area = π/4 × 12.5² = 122.7 mm². UTS = 40 000 / 122.7 ≈ 326 N/mm² (MPa). Elongation = (62 − 50)/50 × 100 = 24 %. Together these show a ductile, medium-strength steel.
Traps
- Dividing by diameter instead of area.
- Calculating % elongation on the final length; it is always on the original gauge length.
- Confusing malleability (sheet) with ductility (wire).
- Calling cast iron ductile - it is brittle.
- Mixing Brinell (ball indenter, HB) with Rockwell (cone or ball, HRC).