Modeling of dynamic crack propagation using rate dependent interface model

Influence of crack tip separation rate-dependent cohesive zone modeling at mesoscale and macroscale behaviors are investigated for sub-Rayleigh, intersonic and sub-Rayleigh to intersonic dynamic delamination growth speeds. A simple rate-dependency factor, k, is proposed for bilinear cohesive zone model (CZM) using the interface model of Corigliano et al. (2006). The factor is defined by the ratio of dynamic to static fracture toughness which is found to be related to the square of the ratio of pure-mode interfacial strengths for the selected bilinear CZM. Experimental cases from the literature with different loading rates are parametrically studied by varying the rate-dependency factor from unity, which is rate-independent, to infinity, a non-physical but theoretical condition. The first case is the three-point impact bending test that exemplifies the low-speed mode-I dynamic fracture. Next, asymmetric impact loading of polymer-composite experiment providing a mode-II dominated high speed intersonic propagation is simulated with various k. After comparing with mode-I low speed and mode-II dominated high-speed dynamic fracture experiments, an parametric analysis is carried out for a mixed-mode sub-Rayleigh to intersonic dynamic delamination in composite L-beams and compared with the experiments from Gozluklu et al. (2015). For this case, it is observed that the macroscopic aspects of fracture do not change with the rate-dependency factor. The effect of rate-dependency on crack growth kinetics is also found to be negligible for crack initiation and early stages of propagation, although the energy release rate increases. For one of the crack tips growing at intersonic speeds, the crack tip slows to sub-Rayleigh as the rate-dependency factor goes to infinity. The crack tip speeds for k > 1 provides slightly better results compared with the experiments. In conclusion, rate-dependency is observed to be necessary in accurately modeling low speed, and low-to-high speed crack propagation cases but not in high-speed intersonic crack propagation.