On the calculation of energy release rate for viscoelastic cracked laminates

Generally speaking, the crack in viscoelastic materials will grow in some unknown speed even if the applied load is quasistatic, thus the main difficulty is induced in deriving the energy release rate. In this paper, we redefine the energy release rate (ERR) of crack growth as the energy change at the same time t between the two states of the structure, one is with crack length a under the loading /spl sigma/(t), the other is the state with crack length a+/spl Delta/a under the same loading condition. Thus the defined energy release rate corresponds to the released energy when a crack grows suddenly from a to a+/spl Delta/a. It is found that under a given loading history, the ERR is a function of time, and its maximum value should correspond to the critical state for delamination to propagate. Following William's work, the explicit expressions of ERR for DCB experimental configurations to measure the interfacial fracture toughness have been obtained through the classical beam assumption.