brittle

Brittle describes a material's tendency to fracture with little or no plastic deformation when subjected to stress. In contrast to ductile materials, which deform plastically before failure, brittle materials crack and fail abruptly, often with minimal warning. Brittleness is not an inherent fixed property; it varies with temperature, strain rate, and microstructure.

Common brittle materials include window glass, ceramics, concrete, and many cast metals. These materials typically exhibit low toughness and low fracture energy, so cracks can propagate rapidly under stress. In many cases, failure is governed by fracture mechanics rather than yield strength; the stress intensity factor and crack length determine critical conditions for rapid fracture.

A range of factors influences brittleness. Lower temperatures tend to increase brittleness in many steels and polymers; higher strain rates can reduce plastic flow; microstructural features such as large flaws, coarse grains, or brittle phase constituents promote crack initiation and propagation. Alloying, heat treatment, and added toughening mechanisms can reduce brittleness, while certain composites exhibit high toughness despite brittle constituents.

Measurement often involves impact or fracture toughness tests, such as Charpy or Izod tests, and the fracture toughness parameter K_IC. Design strategies to mitigate brittleness include avoiding sharp corners and stress concentrators, controlling temperature, using tougher materials or fiber-reinforced composites, and incorporating redundancy.

In everyday language, brittle also describes objects or behavior that are fragile or easily broken, such as a brittle glaze or a brittle temperament, though this usage is metaphorical rather than technical.