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Analysis of Process-Induced Residual Stresses in Tape Placement

The tape placement for thermoplastic composites involves heating, melting, and cooling steps just as do the other manufacturing processes. Consequently, development of residual stresses is unavoidable due to disparate thermal characteristics of matrix and fiber materials and also due to nonuniform cooling rates. From the product quality standpoint, such as interlaminar strength, dimensional accuracy etc., these stresses should be kept within allowable limits. In this study, a thermoviscoelastic finite element model was developed to predict residual stresses induced during the placement of thermoplastic composite tapes. The process, being continuous, was considered to be under a quasi steady state where process conditions do not change with respect to the moving roller. Relaxation of the residual stresses in previously laid layers was also allowed for. Results were obtained for both unidirectional and cross-ply laminates. They show the residual stress distributions through the thickness for a number of chosen sets of process parameters (e.g., roller velocity and heat input). Therefore, residual stresses in a laminate can be controlled by modifying these process parameters.