Compression strength of stitched foam-core sandwich composites with impact induced damage

Compression-after-impact responses of sandwich structures composed of stitched foam core and woven face sheets have been investigated experimentally and numerically. In the impact experiment, the force-time curves are recorded and analyzed to study the impact response of stitched foam core sandwich structures. In the compression-after-impact test, the damage mechanism of stitched sandwich structures during compression loading is revealed. The compression cracks start from the impact-induced damage location and propagate perpendicular to the compression direction. The final failure of the structure is controlled by the crush of the woven skin in the upper panel. For the relatively densely stitched foam sandwich, more fiber resin columns embed in the stitched samples decrease the impact-induced damage in upper panel when subject to impact load and increase the stiffness and strength of the foam in the compression direction during the compression-after-impact test, causing an increase in compression strength of relatively densely stitched sandwich. The relationship of compression-after-impact strength with stitching density appears linear when the impact energy is small, since there is no perforation or penetration. In numerical simulation, multi-scale approach has been developed on evaluating the compression-after-impact strength of sandwich structures. The classical theory of homogenization is adapted and used by treating the foam strengthened by the glass fiber resin column as orthotropic equivalent core material whose elastic properties depended on each component and their volume participation. Then, a nonlinear finite element model using this approach is proposed. Good agreements between finite element model and experiment are found.