Process-Induced Stress Relaxation Analysis of AS4/3501-6 Laminate

In this study the cure-dependent stress relaxation of 3501-6 epoxy resin was analyzed. To formulate the constitutive equations, several stress relaxation tests were performed at different degree of cure states. The master curve and shift function for each degree of cure case were obtained by time-temperature superposition. On the basis of this data, the thermorheologically complex behavior of 3501-6 epoxy resin was modeled. The resin model was then used to formulate the constitutive equations for AS4/3501-6 composite. A finite element method was then used to calculate the interlaminar stress relaxation at the free edge of AS4/3501-6 cross-ply laminates during cool down from the cure temperature. The relaxation behavior of 3501-6 epoxy was shown to be dependent on the degree of cure and significant reduction in residual stress was found to occur at a modest (2.5°C/min) cool down rate.