Inter-laminar and intra-laminar damage evolution in composite panels with skin-stringer debonding under compression

In this paper, a numerical investigation on the inter-laminar and intra-laminar damage mechanisms, characterising the skin-stringer debonding growth in stiffened composite panels subjected to compressive load, has been carried out. A novel numerical methodology for inter-laminar damage growth simulation, based on VCCT technique and able to overcome mesh and time step sensitivity issues, has been adopted in conjunction with a User Material Subroutine (USERMAT), based on Instantaneous Degradation Models (IDM), to investigate the influence of the intra-laminar damages, in terms of fibers and matrix failures, on skin-stringer debonding evolution. The proposed numerical model has been applied to two configurations of single stiffener composite panels with different geometry and debonding size. The numerical results, in terms of compressive load as a function of applied displacements and debonding evolution up to failure, have been compared to experimental data to assess the effectiveness of the implemented methodology. A further comparison with a previously developed numerical model, taking into account only the inter-laminar damage growth, has allowed assessing the influence of the intra-laminar damage on the skin-stringer debonding propagation and the benefit of the proposed integrated inter-laminar intra-laminar numerical model.