Analysis and optimisation of multistable composites under residual stresses

Abstract

During the manufacturing process of multilayered fibre-reinforced composites with variable fibre orientations, residual stresses build up due to the directional expansion of the unidirectionally reinforced single layers. Dependent on the laminate lay-up, these inhomogeneous residual stresses, which are caused by thermal effects, moisture absorption and chemical shrinkage, can lead to large multistable out-of-plane deformations in case of unsymmetric laminates. Instead of avoiding these laminate's curvatures, they can be advantageously used for technical applications such as near-net-shape technologies or adaptive structures. In order to adjust the deformations to technical requirements, a dimensioning tool consisting of an advanced stability and failure analysis in combination with a novel optimisation procedure has been developed. This tool, based on a non-linear calculation method, enables the purposeful adaption of the laminate lay-up dependent on the loading and process parameters and is furthermore the basis for the design of novel adaptive structures.