Combined Effect Of Damage And Thermal Softening With Application To Welds Under Dynamic Loading

摘要

Several years ago an extensive series of well-instrumented tests was conducted by Giovanola et al in which explosive loads were used to induce ductile fracture in weldments at the base of stiffeners. The fracture path consistently started at the edge of the heat-affected zone (HAZ) and progressed directly through the baseplate. Using the finite element code LS-DYNA, it was shown that a local damage criterion, based on erasing elements achieving a critical level of strain-dependent damage, was capable of predicting the correct fracture path. The model was very limited in assuming isothermal, rate-independent response, and assuming isotropic hardening. It is well known that both thermal and damage 'softening' occur, but the two effects do not appear to have been combined in previously published local criteria. The present study introduces a local damage model, which accommodates adiabatic response in which inelastic work is converted into heat. The model likewise integrates thermal and damage softening, includes rate dependence, and accommodates kinematic hardening. It has been implemented in LS-DYNA and used to simulate the Giovanola configuration. The material parameters are taken from the literature and are thought to be realistic. The correct fracture path is again predicted. But the predicted thresholds are found to be significantly reduced from Giovanola's pre-dictions. The combined effects of softening are considerably more severe than either one by itself. Likewise the rate of crack growth is significantly higher. The effect of the model on the fracture path and history are illustrated for symmetric and asymmetric weldments.