Improving the structural integrity of foam-core sandwich composites using continuous carbon fiber stitching

This study aims to improve the structural integrity of foam-core sandwich structures by embedding carbon-fiber/epoxy stitched reinforcements with fiber-volume fraction (V-f) as high as 55 %. Sandwich panels with 1.5 mm thick carbon fiber skins and 30 mm thick PVC foam-core were stitched with 0, 12 k and 24 k carbon fiber yarns. X-ray computed tomography (CT) was utilized to determine the as-manufactured quality of the stitched panels. Flatwise-, edgewise-compression and 3-point bending tests were conducted with in-situ 3D Digital Image Correlation (DIC) to record the deformation and analyze the structure's mechanical response. It was observed that compared to non-stitched samples - under flatwise compression loading, the reinforced samples with a stitch V-f of 0.34 and 0.55 showed an increase in stiffness and strength by 130 % and 163 %, and 29 % and 53 %, respectively. For edgewise-compression and 3-point bending loading cases, stiffness and strength of stitched samples showed an increase of similar to 20 % over the benchmark. Using DIC, X-ray CT and a fractography analysis, the external and internal damage as well as failure mechanisms were evaluated. Analytical solution was employed to understand the parametric influence of the stitch V-f and stitch density per unit area in pursuit of an optimized sandwich structure.

Automated summary

This study improves the structural integrity of foam-core sandwich structures by embedding carbon-fiber/epoxy stitched reinforcements. Experimental results show that the stitched samples have higher stiffness and strength compared to the non-stitched samples under different loading conditions. Furthermore, the external and internal damage as well as failure mechanisms of the stitched samples are evaluated using DIC, X-ray CT, and fractography analysis.