A novel method to measure residual stresses in unidirectional GFRP

A few methods are available for measuring the residual stresses that occur in the simplest of all possible composites structures – the unconstrained unidirectional laminate. None of them, however, are suitable for use on GFRP. A new method is presented whereby the stresses in a unidirectional GFRP laminate can be determined. The method relies on releasing the constraints between fibre and resin through an annealing process. The strain in the glass fibres is thus obtained, which allows the elastic stresses within the fibres and the resin to be determined. In this way, it is not necessary to take account of plasticity and viscous effects in the polymer in order to determine the stresses within the laminate. Results for unidirectional laminates initially manufactured to contain differing residual stresses are presented and discussed.