Crack tip shielding from a plastic 'inclusion'

This paper presents a very brief overview of the philosophy underlying a plastic inclusion approach to defining the boundary stresses imposed on the applied elastic stress or displacement field by the plastic deformation attendant on crack growth in a ductile material. It leads to two new fracture mechanics parameters, K_R and K_S. K_R defines a retardation component arising from wake contact and the Poisson's contraction associated with the plastic zone, whilst K_S describes a compatibility-induced component arising from shear at the elastic-plastic interface. These additional components imply that K_F is not directly comparable with K_I, as it describes the net driving force on the crack from the applied load.