Numerical method to control high levels of damage growth using an implicit finite element solver applied to notched cross-ply laminates

Numerical modelling of composites is becoming ever more important to commercial aircraft manufacturers for design-phase cost reductions and improved lead times. The implementation of a user-defined numerical model for damage prediction in composites is described. All modelling is conducted in ABAQUS/Standard (an implicit solver) and the models demonstrate stable performance with significant levels of damage. This stability is often difficult to achieve when modelling damage with implicit solvers. The favourable performance is due to the damage variable evaluation, which uses information from the previous iteration of an increment to drive damage development during a given load step. This "pseudo-current" damage evaluation is complex to implement, however, the stable performance and the improved time-step size dependence justifies this approach. The method is applied to analyse cross-ply open-hole tension specimens having similar layups but demonstrating different damage growth and varying failure loads. The analysis includes in-plane damage, delamination and splitting mechanisms and a nonlocal regularisation scheme to mitigate spurious mesh sensitivity. The delamination and splitting mechanisms are essential for differentiating between the various specimen types. The damage evolution method provides stability to the implicit solver allowing significant levels of damage to develop within the laminates, giving a valuable prediction of laminate behaviour.