Mesh independent modelling of tensile failure in laminates using mixed-time integration in explicit analysis

A computationally efficient method for discrete modelling of cracks in laminated composite structures using explicit time integration is proposed. Discrete crack modelling involves formation of strong discontinuities and the integration domain of elements must be transformed to include this discontinuity. In explicit time integration, this results in a reduction in the stable time increment of an analysis and the corresponding increase in computational cost limits its application to small scale meshes. Also, remapping of integration domains and initiation of cohesive segments introduces numerical errors in the solution. To solve these two problems, a mixed time integration or subcycling is performed adaptively following element splitting and cohesive segments are initiated with minimal disturbances to the surrounding stress field by nodal force balance. The challenges in the implementation, the effects of assumptions involved in subcycling and its computational benefits are discussed in the context of modelling tensile failure in composite laminates. Modelling of transverse cracks are performed with linear solid elements in unstructured meshes where crack geometry does not align with the initial mesh. To demonstrate its effectiveness, the method is applied to laminates containing an open-hole and a laminate with embedded wrinkles arising from manufacturing defects.