APPLICATION OF ENERGY-DISSIPATION RATE ARGUMENTS TO DUCTILE INSTABILITY

Equations are established for the final macro-unstable behaviour of a fully plastic cracked component in terms of the energy dissipation rate. Control by this first differential of energy occurs when the second differential of the energy absorbed is negative, a condition easily met for crack growth in certain fully plastic cases. The driving force for the instability is a term, I that becomes greater than the lefm term, G, as plasticity occurs. The additional component is an exchange of elastic to plastic energy, a term that is system dependent and is thus the main driving force for a fully plastic ductile instability. A possible relevance to brittle fracture and to a system dependence of both initiation toughness and the whole crack growth resistance curve is discussed.