Strain energy release (Irwin's modification for plane stress)

Description

A fracture is the separation of an object or material into two, or more, pieces under the action of stress.There are three ways of applying a force to enable a crack to propagate: Mode I fracture – Opening mode (a tensile stress normal to the plane of the crack), Mode II fracture – Sliding mode (a shear stress acting parallel to the plane of the crack and perpendicular to the crack front), and Mode III fracture – Tearing mode (a shear stress acting parallel to the plane of the crack and parallel to the crack front).
Irwin showed that for a mode I crack (opening mode) the strain energy release rate and the stress intensity factor are related.