Weak and strong bi-material interfaces and their influence on propagating cracks in plane elastic structures

The developing crack paths in heterogeneous structures are the result of the inhomogeneous state of stress. The latter stems from e.g. voids or inclusions in an elastic matrix, which are bonded either by strong or weak interfaces. Besides the stiffness of an inclusion, the kind of interface has a decisive influence on the state of stress and therefore on propagating cracks. It is experimentally proven that cracks tend to grow towards regions with lower stiffness (Tilbrook et al., 2006; Judt et al., 2015), therefore matrix cracks might be attracted by interface delamination cracks. In this research the matrix crack growth in bi-material structures is simulated, ncorporating dissipative processes arising at weak interfaces and a reference is provided by simulating the crack propagation in the same bi-material but with a strong (perfect) interface. Incremental crack extensions constitute the matrix crack growth, requiring a continuous modification of the geometry. An intelligent re-meshing procedure is applied, where the loading history cannot be neglected due to the presence of dissipative processes (Judt and Ricoeur, 2013b). The crack deflection and crack tip loading are determined by the J-integral criterion and the energy release rate, respectively. The resulting crack paths confirm that the matrix crack tends to grow into the direction of regions with lower stiffness. If weak interfaces are considered, an extremely attracting effect on propagating matrix cracks caused by the delamination is observed, which is stronger than the influence of divergent stiffnesses.