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-d ependent matrix properties was developed to analyze residual stresses in graphite/PEEK composites. The residual stress model takes into acco unt the mismatch of the thermal expansion coefficients and the crystal lization 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 laminate s were manufactured at different cooling rates to verify the model. Th e induced residual thermal deformations were measured by a shadow moir e system. The model estimated the out-of-plane displacement of the non -symmetrical laminates accurately. The optimum processing cycles, whic h minimize the residual stresses and maximize the mechanical propertie s of composite materials, were found to be different for different lay -ups. Therefore, in order to minimize the residual stresses and to opt imize the mechanical performance of the composite laminates, an approp riate processing cycle must be chosen for each specific lay-up.