Elasto-plastic three-dimensional crack border field-III. Fracture parameters

The variations of the amplitude of the stress field, the triaxiality of stress and the crack tip opening displacement against the triaxial stress constraint T₌ are analysed in detail based on the work of Part I and Part II of this study. The concrete form of T₌ in front of a through-thickness crack in contained yielding is proposed and the actual distribution of stresses in the front of elastic-plastic through-thickness cracks is predicted. Good agreement with finite element results confirms the analytical findings. Furthermore, an elastic-plastic fracture criterion, including the effect of crack tip blunting on the parameter characterizing fracture, has been developed and proven to be a material constant independent of plate thickness for a given material state. Both ductile and mixed ductile-brttile fracture have been discussed.