A viscoelastic model for predicting isotropic residual stresses in thermosetting materials: Effects of processing parameters

The isotropic residual stresses in a composite subjected to three-dimension al constraints are calculated by extending a thermo-viscoelastic model deve loped previously by Simon et al. [1] to describe the time, temperature, and conversion dependence of the shear modulus for a commercial thermosetting material during cure. Experimental residual stress data as a function of cu re time are fit to obtain limiting values for the rubbery and glassy bulk m oduli. The effects of cure history on isotropic residual stresses are then investigated via simulations using the bulk moduli, a model of the cure kin etics, the relationship between T-g and conversion, and the stress relaxati on function obtained in the thermo-viscoelastic model which includes the de pendence of the shift factor on temperature and conversion. The isotropic r esidual stresses at room temperature can be directly related to the cure te mperature at which gelation occurred for cases when vitrification does not occur during cure.