Fracture toughness measures a material's resistance to crack advance. In a thin elastic plate model, the threshold for advance can be represented by a prescribed front curvature . Such a curvature parameter is not numerically interchangeable with a bulk fracture-toughness parameter without specifying the fracture model.
Crack growth becomes energetically possible when the energy release rate reaches its critical value. For fixed crack geometry this gives a brittle-failure stress scaling as .
The decrease in potential energy per increment of crack area under specified loading constraints. Its critical value is a crack-growth threshold, not energy stored per specimen volume.
The threshold energy release rate for propagation of a specified crack under specified environmental and loading conditions.
A requirement that a crack penetrate a pressure boundary and produce a detectable leak before unstable fracture. A simple screening comparison uses critical crack size versus wall thickness, but the result depends on crack geometry and on whether stress or pressure is held fixed.
A conservative material-screening upper bound obtained by requiring wall penetration before fast fracture even at a stated yield-limited stress. Substituting a thickness-dependent pressure stress instead yields a different fixed-pressure inequality; the two comparisons must not be conflated.
The reduction in a mechanical system's potential energy per incremental crack area under specified loading conditions. In small-scale-yielding linear elasticity, mode-I plane strain gives with . The critical value includes the dissipative processes associated with crack advance.
A region of irreversible deformation near a crack tip where an elastic singular-field extrapolation would exceed the material's local yielding response. Its size depends on loading and constraint. Plastic work and blunting can raise resistance to crack extension.
An amplitude characterizing a near-tip linear-elastic crack field for a specified loading mode. The mode-I opening factor scales as the displayed expression for a suitable crack geometry factor . It is not itself the local stress, and large-scale plasticity can invalidate a linear-elastic characterization.
Crack propagation predominantly along grain boundaries. Boundary cavities, chemical segregation and environmental attack are possible contributors; fracture appearance alone does not establish which caused failure.
Brittle crack propagation associated with separation along particular crystallographic planes. Cleavage facets and river patterns can help identify the mechanism, while establishing its cause requires material, loading and exposure evidence.
A change from predominantly ductile deformation and fracture to predominantly brittle fracture as temperature decreases under specified loading and specimen conditions. A quoted transition temperature depends on its criterion: absorbed impact energy, fracture appearance and fracture toughness need not give the same number. In ferritic steel, irradiation hardening can raise the transition temperature.
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Fracture toughness is a property of materials that measures their ability to resist crack propagation when subjected to stress. It quantifies the material's resistance to fracture in the presence of pre-existing flaws such as cracks or voids. Fracture toughness is expressed as a critical stress intensity factor (K_c), which combines the effects of the applied stress, the size of the crack, and the material's properties.