Failure Mechanisms

Griffith theory of Brittle Fracture

· Griffith postulated that brittle fracture results from the rapid propagation of pre-existing micro-cracks in a material.
· The material becomes unstable when the increase in surface energy due to the creation of new crack surface equals the decrease in stored elastic energy in the sample through stress relaxation as the crack propagates.
· Experiments by Orowan on mica and by Griffith on glass supported the existence of microcracks.

s_F1 < s_F2 < s_F3