Accurate coarse mesh simulation of delamination in composites using a novel hp-adaptive cohesive element

Cohesive elements are routinely used to simulate delamination between plies in composites. However, the allowable maximum size of these elements is limited, owing to the presence of a very small process zone ahead of the cohesive crack-tip, which needs to be discretised with multiple elements for obtaining an accurate failure response. This restricts their applicability beyond analysing delamination in coupon scale problems, due to the need for a very fine mesh and associated large problem size. In this paper, a novel hp cohesive element is developed to address this problem. This element is capable of simultaneous mesh refinement and elevation of interpolation order, locally and adaptively around the propagating cohesive crack tip. Additional degrees of freedom associated with the hp refinement are handled by extra nodes already supplied in the initial mesh file, that are selectively activated by the program as required. Several example problems are presented showing the ability of this method to improve the prediction of delamination onset and growth in extremely coarse meshes with a reduced computational time.