Nonlinear viscoelastic finite element analyses of thermosetting polymeric composites during cool-down after curing

Thermally induced stresses that occur during the cool-down process after curing are investigated on the basis of nonlinear thermo-viscoelastic finite element methods. Nonlinear viscoelastic stress singularities near free edges of laminated composites are evaluated as a function of time and cool-down history. Various cool-down histories are considered. Temperature distributions inside composites are predicted by solving heat conduction equations. Numerical results indicate a strong sensitivity to the nonlinearities of viscoelastic constitutive relations. Temperature history significantly affects residual interlaminar and in-plane stresses. The rate of stress relaxation also varies with the loading history.