Residual Stress Quantification Using Asymmetric Laminates

Abstract The curvature and stress-free temperature derived from asymmetric specimens after manufacturing can be used to quantify residual stresses in FML laminates. Several intrinsic and extrinsic parameters influence the accuracy of this experimental method. To determine the residual stress state in one principal direction, specimens with a small width-to-length ratio are preferred. Using three-dimensional curvature or stress-free temperature measurements in a lab oven provides accurate process-specific parameters from which the residual stress state can be derived. The accuracy is in the same order of magnitude compared to measurements using integrated sensors. Since the stress-free temperature is a parameter that is independent of the specimen layup, it can be directly transferred to laminates with other layups, including symmetrical ones. The only restriction is that the extrinsic parameters influencing the residual stress development in asymmetric specimens are not scaling with specimen size and that the manufacturing conditions (e.g. prepreg material, tool material, vacuum bagging setup, temperature profile of the cure cycle) are the same for both layups.