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SUMMARYThrough-the-thickness crack propagation in thin-walled structures is dealt with in this paper. The formulation is based on the cohesive zone concept applied to a kinematically consistent shell model enhanced with an XFEM-based discontinuous kinematical representation. The resulting formulation comprises the representation of continuous deformation, represented by midsurface placement, director and thickness inhomogeneous fields, and discontinuous deformation, represented by discontinuous placement and director fields. The shell model is implemented both for the implicit static analysis and in the context of explicit dynamic integration pertinent to impact loading, and the implementation results in a 7-parameter solidshell element based on a 6-noded triangular element. In order to properly formulate the dynamic fracture characteristics, a rate-dependent cohesive zone model is employed with respect to, e.g. limiting crack speeds as observed experimentally. In the final example, this model has been applied to a blast loaded pressure vessel that has been experimentally tested. The results indicate that the right crack speed as well as fracture characteristics are relatively well captured. Furthermore, it appears that the discontinuous model exhibits the expected properties with respect to critical time step size in the dynamic analysis and convergence behavior towards the analytical static solution.

SUMMARYA combined approach towards ductile damage and fracture is presented, in the sense that a continuous material degradation is coupled with a discrete crack description for large deformations. Material degradation is modelled by a gradient enhanced damage-hyperelastoplasticity model. It is assumed that failure occurs solely due to plastic straining, which is particularly relevant for shear dominated problems, where the effect of the hydrostatic stress in triggering failure is less important. The gradient enhancement eliminates pathological localization effects which would normally result from the damage influence. Discrete cracks appear in the final stage of local material failure, when the damage has become critical. The rate and the direction of crack propagation depend on the evolution of the damage field variable, which in turn depends on the type of loading. In a large strain finite element framework, remeshing allows to incorporate the changing crack geometry and prevents severe element distortion. Attention is focused on the robustness of the computations, where the transfer of variables, which is needed after each remeshing, plays a crucial role. Numerical examples are shown and comparisons are made with published experimental results.

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