Tensile stiffness distribution in impacted composite laminates determined by an inverse method

The constitutive properties of impact damage zones in composites are determined by iteratively matching an FE model to displacement fields measured optically during post-impact loading. The method is validated on a reference FE model with axisymmetric damage containing four concentric zones having different properties, and examines the influence of measurement noise. Real impact damage zones in quasi-isotropic carbon/epoxy laminates under tension are then analysed and compared to fractography by C-scan to detect delaminations and deplying to detect fibre fracture. Tensile stiffness gradually decreases towards the damage centre, but stiffness reductions are confined to a small central region with fibre fracture.