Residual-Stress-Analysis within composites

For evaluation of residual stresses in isotropic material commonly the ASTM E837 is used. There is no such analytical solution for anisotropic material such as for composites. It requires FEM simulations to couple the measured surface deformation to the released stresses inside the material whereby the FEM simulation must consider the unidirectional laminate structure. This example here shows the results of a Cycom 977-2 carbon fiber UD prepreg material- two different curing cycles and four different layup s (0/90/0/90)s.

The FEM simulation is adapted and validated via the computed surface strain or deformation field in comparison with the ReSA measurement at different drilling depth (Fig. 1). This information is used to determine the residual stress inside the structure as shown in the table and image (Fig. 2). The simulation is done by the IVW, University Kaiserlautern, Germany.