Engineering Materials and Material Testing
Engineering Materials and Material Testing examines how the choice of metal is matched to service, and how standard tests prove the properties. You need the ferrous and non-ferrous families, heat treatment, and the tensile and hardness tests with their numbers.
Core rules
- Carbon content drives steel behaviour: mild steel ≈ 0.15–0.30 % C (ductile, weldable), medium carbon 0.3–0.6 % (hardenable), high carbon 0.6–1.4 % (springs, tools). Grey cast iron has 2–4 % C as flakes and is brittle but damps vibration well.
- Non-ferrous: aluminium (light, protective oxide film), copper (conductivity), brass = Cu + Zn, bronze = Cu + Sn, zinc for galvanising.
- Tensile test on a UTM gives yield strength, ultimate tensile strength (UTS) and percentage elongation; the last is a ductility measure that depends on gauge length.
- Hardness: Brinell uses a 10 mm ball at 3000 kgf (HB); Rockwell C uses a diamond cone at 150 kgf (HRC); Vickers uses a diamond pyramid and suits thin sections.
- Heat treatment: annealing (soften, slow furnace cool), normalising (air cool, refine grain), hardening (quench), tempering (restore toughness after hardening).
Worked example
A tensile specimen of diameter 10 mm and gauge length 50 mm breaks at 40 kN and the final gauge length is 60 mm. Area = π × 10²/4 = 78.5 mm². UTS = 40,000 N ÷ 78.5 mm² = 510 N/mm² (MPa). Elongation = (60 − 50)/50 × 100 = 20 %, a ductile result.
Traps that cost marks
Quoting UTS when the question asks for design (yield) stress; using Brinell on thin sheet; mixing up annealing and normalising cooling; forgetting that % elongation depends on gauge length; treating cast iron as weldable steel.