Innovative test methodology for shelf life extension of carbon fibre prepregs

The aerospace industry makes extensive use of composite materials in the form of fibre fabrics pre-impregnated with thermosetting resin, called prepregs. In order to minimize the resin polymerization before curing, prepregs must be stored at -18°C (0°F). There are therefore expiration dates for prepregs before use. Although manufacturers try to minimize storage time, offcuts and time out of the freezer, it is estimated that 30% to 40% of the prepregs are not used [1]. Today, recertification of expired materials is still complex and expensive, therefore it is generally chosen to send expired prepregs to landfill. The purpose of this work is to correlate physicochemical measurements with the loss of mechanical performance in order to point out and measure the real aging effects during excessive storage time. Processability, physicochemical and mechanical tests were performed in order to understand which tests are truly representative of ageing. This study was illustrated by testing on unidirectional Hexcel carbon/epoxy prepreg. Different expiry dates of this material were studied and the properties were compared. It was shown that the main observed degradation was the processability of the prepreg while mechanical performance was minimally degraded after the expiry date. This study could lead to a simpler measurement of the actual expiry rate of prepregs, which could be useful to speed up recertification procedures or to propose new scenarios to extend the shelf-life of expired prepregs [2].