Mesoscale modelling of extended bearing failure in tension-absorber joints

This paper presents the development and validation of a mesoscale composites damage model for predicting the energy absorption capability of “tension-absorber” joints. Tension-absorber joints are composite bolted joints specially designed to absorb energy in a crash via “extended bearing failure”, which involves the bolt forcing its way through the composite over a long distance. They have been proposed for use in future narrow-body composite fuselages. Here, extended bearing failure tests on a carbon fibre/epoxy laminate, are simulated using explicit three-dimensional finite element analysis. A physically based damage model is implemented in a user-defined subroutine. The model uses in-situ ply strengths, stress-based fibre failure criteria, Puck's criteria for matrix damage, a nonlinear law for in-plane shear, a cohesive zone model for delamination, a crack band model to mitigate mesh sensitivity, and frictional contact between the pin and the laminate, and between adjacent plies once they delaminate. The model is found to accurately predict the global response, in terms of bearing strength, mean crush stress and energy absorption, and comparison with CT scans shows that it also captures the mesoscale damage very well. The model is used to predict the effects of pin diameter, laminate thickness and stacking sequence, and the results show excellent agreement with experimental findings.