Novel epoxy powder for manufacturing thick-section composite parts under vacuum-bag-only conditions. Part II: Experimental validation and process investigations

Validations of a one-dimensional process model are carried out by manufacturing thick-section glass-fibre reinforced composite laminates with a low-exotherm epoxy powder. An experimental apparatus is developed which heats the laminates from one side while insulating the remaining sides (i.e. approximating one-dimensional heat transfer conditions). The experimental results are analysed and used to validate process models for the epoxy powder system. Process simulations are performed to analyse the influence of material format, laminate thickness change, and heating methods (i.e. one-sided heating vs two-sided heating, and heated tooling vs oven heating). It is shown that epoxy powder eliminates the risk of ‘thermal runaway’, but thermal and cure gradients persist for a conventional processing cycle. Methods to inhibit the evolution of these gradients are explored using process simulations. These methods include modifying the temperature cycle and using multiple epoxy powders with varied latent curing properties.