Stress-strain graph
A graph of stress (force per unit area) on the y-axis versus strain (proportional change in length) on the x-axis, showing how a material deforms under load. The graph reveals elastic behaviour (straight-line region), yield point, plastic deformation, and ultimate tensile strength.
Formula
E = gradient = σ/ε (in linear region)
Real World
Materials scientists at Rolls-Royce use stress-strain graphs to compare turbine blade alloys, selecting materials whose graphs show a steep gradient (high stiffness) and large fracture strain (high toughness).
Exam Focus
Label all key points — limit of proportionality, elastic limit, yield point, UTS, and fracture — examiners award a mark for each correctly identified feature.
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