The measurement and prediction of residual stresses in carbon-fibre/polymer composites

Experiments have been carried out that measure the residual stress in a thermoplastic matrix and a toughened thermosetting matrix, both reinforced with carbon fibre. Some of these experiments are based on the determination of the extent of curvature of unbalanced laminates as they cool from their processing temperature to ambient conditions. Other experiments involve measurements of the first-ply cracking stress. Both methods are compared and modelled by using classical lamination theory. It was demonstrated that, under certain conditions, the residual tensile stress can approach closely to the transverse ply tensile strength. After 200 days at ambient conditions, these stresses can decay by approximately one-quarter.

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