brittleness

Brittleness is the tendency of a material to fracture under stress with little to no plastic deformation. It is a failure mode characterized by sudden fracture rather than gradual yielding.

Brittleness is inversely related to ductility and toughness. Ductile materials deform plastically before failure, showing necking and significant energy absorption. Brittle materials crack and fracture with minimal deformation, absorbing relatively little energy. The overall resistance to fracture is described by toughness, the energy required to propagate a crack, or by fracture toughness, a property that characterizes a material’s resistance to crack growth.

Causes and mechanisms vary with microstructure, temperature, and loading conditions. Brittle fracture often occurs by cleavage along crystallographic planes or by intergranular cracking, especially in ceramics and glasses or in metals at low temperatures or under high strain rates. The presence of flaws, residual stresses, and environmental factors such as hydrogen can enhance brittleness, a phenomenon known as hydrogen embrittlement or temper embrittlement in some steels.

Common brittle materials include glass, ceramics, cast iron, and some polymers at low temperatures. Metals may behave in a brittle manner at cryogenic temperatures or during rapid loading, while many metals become more ductile with increasing temperature (a brittle-to-ductile transition).

Testing and design considerations aim to quantify and mitigate brittleness. Impact tests (Charpy or Izod) assess toughness, while fracture toughness tests measure resistance to crack growth. Design strategies to reduce brittleness include avoiding sharp corners and large flaws, selecting more ductile materials, and employing toughening techniques such as grain refinement, tougher phases, or controlled microstructures.