Multi hardener laminates: A novel approach to optimize thick composite cure

Due to the exothermal cure reaction of the resin and its low thermal conductivity there is an increasing risk for heat accumulation and uneven cure in thick composite laminates. In this study a novel approach to reduce overshoot, cure degree gradient and process time based on the usage of dissimilar resin systems throughout the laminate is explored. An experimentally validated FEM-Simulation was integrated into a multi-objective optimization algorithm and used to choose fitting cure agents, cure agent distributions and cure cycles for 25 mm, 50 mm and 100 mm thick glass fiber reinforced laminates. The algorithm was modified to be able to choose between one anhydride and two amine curing agent while also being able to add accelerator to the anhydride. The resulting Pareto sets show that using dissimilar cure agents in the inner and outer layers of a laminate can be beneficial in terms of cure degree gradients at shorter process times. The biggest improvements were found when varying the accelerator concentration of anhydride cure agent. Here reductions in cure degree gradient of 43 % can be achieved. It was also found that minimizing overshoot and process time alone does not result in the most even cure when using multiple curing agents within a laminate. Generally, choosing a well-suited cure agent and optimizing the cure cycle shortens process times and lowers temperature overshoots and cure degree gradients.