Experimental and numerical study on the tensile failure behavior of toughened-interlayer composite laminates with automated fiber placement (AFP) induced gap and overlap defects

Predictive computational modeling of the effect of automated fiber placement (AFP) defects on the structural performance of aerospace structural composites is of importance in preliminary design. A finite element method (FEM) based framework is presented for the analysis of the quasi-static tensile response of quasi-isotropic [45/0/ - 45/90](2s) laminates containing controlled gaps and overlaps in the 90 degrees plies with different defect sizes (1/2 '', 1/4 '', 1/8 '', 1/16 ''). Consolidated ply geometries were obtained from micro-graphs of actual fabricated specimens in order to capture the effect of out-of-plane misalignments induced by these imperfections. The FEM models were generated in Abaqus CAE with a Python script, in a ply-by-ply manner. The material model for the virtual testing is a multiscale continuum progressive damage and failure model (MCDM), in which the prepeak nonlinear response is based on multiscale micromechanical formulations and the postpeak meso-scale response is modeled with the crack band method (CB). The FEM results were compared to experimental results and showed good agreement in failure modes and mechanical response. The ultimate tensile strength was predicted with reasonable accuracy for most of the cases. With both experimental and numerical analyses, this paper provides a better understanding of the progressive tensile failure of toughened composites (T800S/3900) with gap and overlap defects.