The Effect of Aged Materials on the Autoclave Cure of Thick Composites

Abstract

In order to control the quality of composites fabricated from prepreg, specifications are available for shelf life and out time for various material systems. Once the shelf life has been exceeded, the prepreg must either pass acceptance tests or be disposed of. The objective of this work is to determine the lifetime of prepregs by evaluating the effect of aging on the curing of thick composites. The investigation is carried out by applying numerical simulations of the curing process for graphite/epoxy AS4/3501-6 composite laminates of 3cm thickness. The results indicate that fairly uniform compaction can be achieved in 3cm laminates when using prepreg with up to 10% initial curing. However, large nonuniformity in fiber volume fraction occurs when using prepregs with initial curing of 20% and 30%. In addition, the incomplete compaction that occurs when using initially cured prepregs causes large temperature overshoot during cure despite the lower heat of reaction.