Computational analysis of dynamic crack propagation along a bimaterial interface

Several features of the characteristics of a crack dynamically propagating along a bimaterial interface are investigated and their results are presented in this paper. The stress intensity factors of interface crack dynamics are accurately extracted from finite element field solutions using a new conservation integral. This integral is based on the steady-state solution for a dynamically propagating interface crack. It extracts the Mode I and II contributions of the mixed-mode cracktip field. The ratio of the mixed-mode factors, or the phase angle is an essential parameter in defining the fracture resistance of dynamic interface cracks. A computational analysis is carried out for an interface crack in an infinite plane under either remote tensile or shear loading. The phase angle and the energy release rate of the growing interface crack with different crack-tip velocities are obtained for several bimaterial combinations. For a short time after the initiation of a growth, the energy release rate and the phase angle are found to be very sensitive to the crack-tip velocity. They are much less sensitive to the mismatch in bimaterial properties. At late time, the phase angle merges closer to the corresponding quasi-static values. A toughness formula based on critical energy release rate is proposed for the dynamic interface crack. This toughness criterion is implemented in a newly developed iterative procedure for computing crack propagation. With this procedure, the simulation of crack propagation exactly follows the condition specified by the toughness function. No artificial input or prior knowledge of the crack-tip velocity history is necessary. This is an effective method which can be used to interpret experimental data. We have employed this iterative technique in the simulation of published data for dynamic interface crack propagation to identify a correct toughness formula. The analysis shows that the resulting velocity history agrees well with the experimental record when appropriate parameters are chosen for the proposed toughness criterion.