On the Response of Stitched Woven S2-Glass/Epoxy Composites to High Strain Rate Compression Loading

Abstract

Experimental investigations were carried out to understand the response of stitched/unstitched S2-Glass/SC-15 epoxy composites to high strain rate compression loading using a Split Hopkinson Pressure Bar set-up. Fifteen layers of plain weave S2-glass fabric were used to fabricate stitched/unstitched laminates with a low viscosity room temperature curing SC-15 epoxy resin system. For stitching, a 3-cord Kevlar thread was used. The fabric preforms were stitched through the thickness in a lock-stitch pattern, maintaining a pitch of 6 mm. The fabric was stitched along the length and width, forming a 25.4 mm stitch grid. Four different types of samples were considered. Sample configuration was designated according to the location of the stitch line with reference to the loading direction. Dynamic and static responses of the laminate under compression were compared. Failure modes were studied using optical microscopy. For high strain rate loading, samples of dimension 22.5 × 22.5 × 9.5 mm were tested at five different pressure settings of the Hopkinson Bar Set-up. Results were analysed in terms of peak stress, strain at peak stress, modulus and failure modes. Results of the study showed that, under higher strain rates loading, the stitched laminates exhibited a confining effect. The primary mode of failure for unstitched samples was fibre microbuckling with multiple delaminations. For stitched samples, fibre microbuckling and micro-delaminations were the major modes of failure and were contained within the bounds of the stitch. Overall, stitched laminates will provide increased damage resistance, which will prove very crucial under crash situations.