The effect of cooling rate on free-edge stress development in semi-crystalline thermoplastic laminates

A numerical model is developed for prediction of the process-induced thermal residual stresses in thermoplastic composite laminates. The model addresses the development of the three-dimensional residual stress state in fracture-critical free-edge regions as well as through-thickness stress variations. The current approach and analysis provide a unique capability for the investigation of the influence of thermal processing and structural parameters on the resulting buildup of residual stresses during manufacturing. Therefore, it can assist in the design and analysis of thermoplastic composites in terms of tailoring of mechanical and strength characteristics. The applied surface cooling rate from the melt has a strong effect on the free-edge stress levels obtained at room temperature, and in particular the interlaminar stresses. Results are shown for the case of typical cross-ply and quasi-isotropic APC-2 (graphite/polyetherether-ketone) laminates.