Fatigue

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.

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.

The progressive extension of an existing delamination between the plies of a laminate under cyclic or sustained loading. It is a central concern in damage-tolerant design of laminated structures and is characterised using interlaminar fracture toughness testing.

Slow, time-dependent deformation of a material under sustained load. Polymers and adhesives creep far more readily than metals, particularly at elevated temperature or as the glass transition temperature is approached, so long-term loads must be assessed separately from short-term strength.