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-dimensional constraints are calculated by extending a thermo-viscoelastic model developed 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 cure time are fit to obtain limiting values for the rubbery and glassy bulk moduli. The effects of cure history on isotropic residual stresses are then investigated via simulations using the bulk moduli, a model of the cure kinetics, the relationship between T-g and conversion, and the stress relaxation function obtained in the thermo-viscoelastic model which includes the dependence of the shift factor on temperature and conversion. The isotropic residual stresses at room temperature can be directly related to the cure temperature at which gelation occurred for cases when vitrification does not occur during cure.