Cure-induced residual strain build-up in a thermoset resin

The formation and the build-up of process-induced stresses and strains have been investigated both experimentally and numerically, analyzing the non-isothermal cure of a thermoset polymer resin placed into a rectangular mold. In particular, a stress model has been formulated accounting for the evolution of the resin mechanical properties, the mold constrains, thermal expansion effects and shrinkage phenomena induced by the cure reaction. The mechanical equilibrium equations, based on the Cauchy–Navier approach, have been solved by implementing a finite element code based on an incremental transient approach that reduce the difficulty of defining the stress free conditions. The effect of the mold material on the process induced strain field has been investigated performing numerical simulations both with an aluminum and a steel mold. In addition, the model results have been validated by comparing with the experimental strain measurements which were obtained by embedding a single fiber optic Bragg grating sensor within the resin and activating the polymerization reaction in an oven. Residual stresses and strains have been computed numerically performing two-dimensional simulations on the top and side sections of the experimental mold/resin system. In both cases, a good agreement between the numerical strain results and the experimental fiber optic Bragg measurements was found.