Stress concentration

Progressive, localised damage caused by repeated or fluctuating loads at stresses below a material's static strength. Fatigue governs the life of components such as wind turbine blades, hulls and airframes, and typically initiates at stress concentrations.

A material's resistance to the propagation of a crack from an existing flaw. It underpins damage-tolerant design, and in laminates the related interlaminar fracture toughness describes resistance to delamination growth.

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.