Deformation and fracture mechanisms of automated fiber placement pre-preg laminates under out-of-plane tensile loading

This study concerns the effect of AFP process-induced microstructure and imperfections on the failure response of composite laminates subjected to out-of-plane tensile loading. Microstructure-based description and analysis of automated layup and forming of laminates are firstly conducted by experimental observation. Further, two failure modes are experimentally obtained for understanding the fracture mechanisms of the AFP laminates under out-of-plane tensile loading. In order to capture transition zones of the random gaps and their developments, a two-step approach for constructing a more realistic geometrical model is presented, thereby establishing an AFP random gap model to account for the deformation and failure mechanisms of the out-of-plane tensile specimens. Numerical results show a good agreement with experiments in terms of material modulus and strength and in predicting the failure behavior. In addition, parametric studies show significant knockdown in out-of-plane tensile properties due to gaps, specifically with larger gap sizes showing higher knockdown.