On residual stress induced distortions during fabrication of composite shells

Channel or angle components are important structural members. It has been observed that during the manufacture of these components, residual stresses build up. The state of residual stress in these components leads to a reduction in the enclosed angle where the out-of-plane contraction is higher than the in-plane contraction. This phenomenon (of the reduction in the enclosed angle) is referred to as spring-in. The residual stresses, in addition, may lead to defects such as micro-cracking, delamination, etc. The degree of spring-in and the residual stresses may be estimated by analysing the curved portions of these structural components as sectors of circular cylindrical tubes (see Figure 1). In this paper, a simple mechanics-based model is developed using modified shell theory that predicts the degree of spring-in and determines the stresses and strains in cylindrical segments with arbitrary lay-ups subjected to random temperature gradients. The model accounts for the resin shrinkage occurring during curing and also includes the effect of moisture gradients. The accuracy of the present analysis is investigated by comparing predicted results with previously published results.