Engineering Materials and Their Properties
What this domain tests
Engineering Materials and Their Properties tests the link between internal structure, processing and service performance: ferrous and non-ferrous metals, polymers, ceramics and composites, plus the standard mechanical tests used to compare them.
Core rules
- Crystal structure controls behaviour: BCC metals such as ferritic steel are relatively strong but less ductile; FCC metals such as austenitic stainless steel and aluminium are ductile; HCP metals such as magnesium are less formable at room temperature.
- Plain carbon steel: increasing carbon raises hardness and tensile strength but lowers ductility and weldability. The eutectoid composition is about 0.8% C.
- Heat treatment: annealing softens and relieves stress; normalising refines grain size; quenching forms martensite; tempering restores toughness after quenching.
- Polymers: thermoplastics soften on reheating; thermosets cross-link and cannot be remelted; elastomers recover large strains.
- Mechanical properties come from the tensile test: yield strength, ultimate tensile strength (UTS), Young's modulus and percentage elongation. Hardness is a separate surface-resistance measure, not a substitute for tensile strength.
Worked example
A 12 mm diameter specimen with a 50 mm gauge length carries 10 kN and extends 0.05 mm. Area = π(6²) = 113.1 mm²; stress = 10,000/113.1 = 88.4 MPa; strain = 0.05/50 = 0.001; Young's modulus = 88.4/0.001 = 88,400 MPa ≈ 88 GPa. The calculation uses the original area, so it is engineering stress.
Traps
Using radius as diameter; mixing N and kN; quoting UTS as the breaking stress; confusing hardness scales (HB, HV and HRC are not interchangeable); assuming quenching alone gives a tough part without tempering.