Stress-Strain Diagram - Ductile Materials

When a specimen is subjected to loading the length first increases linearly at a slow rate, resulting in an initial straight line with a steep slope on the stress-strain diagram.

Upon reaching a critical stress value, the specimen undergoes significant deformation with minimal increase in applied load, primarily due to shearing stresses causing slippage along oblique surfaces.

With increasing load, the material's diameter reduces at a point, termed—necking. Post necking, even a small amount of load elongates the specimen further until it ruptures.

Yielding is a process where the material starts to deform plastically. The stress at which yielding starts is termed the yield strength, while the stress corresponding to the maximum load is the ultimate strength, and the stress at rupture is the breaking strength.

The stress-strain diagram of structural steel shows constant stress post-yield due to strain-hardening but aluminium's stress increases non-linearly.

The ductility of the material is measured by percent elongation or percent cross-sectional area reduction. Under compression, ductile materials' stress-strain curves diverge at higher strains as necking doesn't occur.