Plane-strain finite element model for process-induced residual stresses in a graphite/PEEK composite

A plane-strain, linear elastic finite element model with temperature-dependent matrix properties was developed to analyze residual stresses in graphite/PEEK composites. The residual stress model takes into account the mismatch of the thermal expansion coefficients and the crystallization shrinkage of the matrix, Good agreement between the reported transverse normal stress data and the modeling result was observed in the analysis of a [0(40)](T) APC-2 laminate processed at a 35 degrees C/s surface cooling rate. Furthermore, [0(10)/90(6)](T) APC-2 laminates were manufactured at different cooling rates to verify the model. The induced residual thermal deformations were measured by a shadow moire system. The model estimated the out-of-plane displacement of the non-symmetrical laminates accurately. The optimum processing cycles, which minimize the residual stresses and maximize the mechanical properties of composite materials, were found to be different for different lay-ups. Therefore, in order to minimize the residual stresses and to optimize the mechanical performance of the composite laminates, an appropriate processing cycle must be chosen for each specific lay-up.