Fracture toughness

The ability of a material to absorb energy and deform without fracturing, combining strength with ductility. Tough materials resist impact and flaw growth, whereas strong but brittle materials can fail suddenly.

The tendency of a material to fracture with little or no plastic deformation, as seen in glass and many cured thermosets. Brittle materials are sensitive to flaws, notches and impact, and fail suddenly rather than yielding.

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.

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.