Optimal Cool Down in Nonlinear Thermoviscoelasticity With Application to Graphite/Peek (APC-2) Laminates

Many thermoplastic resin composite laminates, such as those made of APC-2, undergo a substantial temperature drop during their post-manufacturing cool down. This thermal excursion induces significant residual thermal stresses into the laminate due to the mutual geometric constraints among the multidirectional plies. In view of the considerable time-dependent relaxation which occurs during the cooling process, the residual thermal stresses exhibit strong dependence on the temperature history. However, in view of the high magnitudes of those stresses, the relaxation behavior is viscoelastically nonlinear. This paper demonstrates that it is possible to obtain an optimal cool-down path which minimizes the residual thermal stresses in APC-2 composites upon the termination of the cooling process.