Stacking Sequence Effects on the Process-Induced Free-Edge Stresses in Thermoplastic Composite 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 residual stress state in fracture-critical free-edge regions as well as through-thickness stress variations. The current approach provides 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 to tailor mechanical and strength characteristics. Thermal processing considered here includes solidification from the molten state at a specific surface cooling rate, and application of a posterior annealing cycle. A significant reduction in the free-edge stresses is obtained via a quench/anneal cycle in comparison to the recommended nominal cooling from the melt. Alteration of the stacking sequence of the plies in the laminate can further reduce the magnitude of the interlaminar stresses. Results are shown for the case of a quasi-isotropic APC-2 (graphite/PEEK) laminate configuration.