Stress

The deformation of a material in response to stress, expressed as change in length divided by original length. Strain is dimensionless, often quoted as a percentage, and may be elastic (recoverable) or plastic (permanent).

A localised increase in stress around a geometric feature such as a hole, notch, sharp corner or ply drop. Stress concentrations are common initiation sites for fatigue cracks and are managed with generous radii, local reinforcement and careful detailing.

Stress locked into a material or assembly in the absence of external load, arising from cure shrinkage, thermal mismatch during cooling, welding or forming. Residual stresses cause distortion, such as spring-in of composite parts, and can add to service stresses to promote cracking.

The maximum tensile stress a material can withstand before failure, determined by pulling a specimen to rupture in a tensile test. It is one of the most widely quoted mechanical properties on datasheets for metals, plastics, laminates and membranes.