Optimization of the wet lay-up/vacuum bag process for the fabrication of carbon fibre epoxy composites with high fibre fraction and low void content

Abstract

It is widely considered that wet layed-up carbon fibre epoxy composites fabricated by vacuum bagging suffer from an inherently high void content compared to autoclaved prepreg systems, and indeed can reach 10% or above in some cases. One reason for this is that the vacuum bag consolidation commonly employed is largely carried out without regard to the viscosity of the resin systems being used. In this investigation the wet lay-up technique is optimized by incorporating a dwell period at the start of the cure cycle to increase the resin viscosity before applying the bagging pressure. Resin viscosity is the critical parameter in producing fibre composites with low void content and a dwell time ‘window’ exists for each resin system within which high quality laminates can be consistently produced with up to 58% fibre volume fraction and less than 2% voidage. The ‘window’ exists between the same viscosity limits regardless of the resin system and temperature being used and therefore can be constructed for any resin system from a knowledge of its viscosity/temperature/time characteristics. The epoxy resins investigated were Ciba Geigy MY750/HY917/DY070 and LY1927/HY1927 with XA-S high strength carbon fibre both in uni- and bidirectional (0/90°) form.