| Dynamic fracture in microlaminates is studied numerically employing the finite element method in a unified framework where the continuum is characterized by two constitutive relations: one relating the stress and strain in the bulk material and the other relating the traction and separation across a specified set of cohesive surfaces. In such a framework, fracture initiation, crack growth, crack trajectory and crack arrest arise naturally as a consequence of the imposed loading, without a priori assumptions concerning criteria for crack growth and for crack path selection.; Attention is focused on fracture in two particular types of microlaminates, bimaterials and lamellar solids. Dynamic fracture in bimaterials is studied, with particular attention to the effect of plasticity on crack growth across the bimaterial interface. It is found that there is a range of strength parameters (flow strength and cohesive strength) for which crack growth behavior deviates from that predicted by quasi-static, elastic analyses. In particular, plastic flow tends to promote crack deflection into an interface strong enough to cause penetration of an elastic adjacent solid.; This thesis also reports the results of studies of fracture in lamellar solids, where two phases of a solid are arranged within a colony in a regular, plate-like manner. Analyses were restricted to cases where one phase is considered to be infinitesimally thin compared to the other. It is found that microstructural features such as vertical and horizontal offsets in the lamellae or a change in the lamellar orientation across a colony boundary can significantly impact the fracture resistance of lamellar solids. The results presented herein show good qualitative agreement with recent in-situ compact tension experiments on binary titanium aluminide (TiAl). |
