Fracture mechanics started with the ideas of Griffith in the 1920s on the fracture of brittle solids such as glass, where he suggested that the fracture strength was inversely proportional to the square root of the length of the largest crack (defect) present. Later in the 1950s, when fracture had been seen in metals without prior plastic (permanent) deformation, the concepts of fracture mechanics were developed. These can be expressed as:

K_Ic = QÛ_fv (_a)
K_Ic = fracture toughness, a function of the material
Q = geometrical factor, related to crack and component geometry
a = length of crack

By analysis of the crack size causing failure and the material, the stress causing the failure can be estimated and compared to the design stresses expected. With the use of fracture mechanics as part of the design process, especially in high strength materials and in high integrity structures, such as aircraft and oilrigs, it is rare to see instant fast fracture.

More usually cracks grow by fatigue (repeated stresses) or stress-corrosion (synergy between tensile stress and corrodant). This crack growth is a function of stress intensity (K_I = QÛv (_a), where Û = stress).