Experimental investigations on the response of stitched/unstitched woven S2-glass/SC15 epoxy composites under single and repeated low velocity impact loading

In the current investigation, damage resistance of stitched/unstitched S2-glass/epoxy composites is studied. Five layer stitched/unstitched plain weave S2-glass woven fabric composite laminates were manufactured using toughened SC15 epoxy resin system. For stitching, two configurations: one with 25.4 mm grid and other with 12.7 mm grid, were used with 6 mm pitch. Damage resistance was evaluated by subjecting 100 × 100 mm samples to low velocity impact loading at energy levels ranging 10–80 J using DYNATUP Model 8210, an instrumented impact test system. Three samples were tested at each energy level. The extent of damage was evaluated using ultrasonic C-scan. Results of the study indicate that stitching confined the damage size. As the damage was low over most of the energy range, the study was further extended to determine the effect of repeated impact loading. Under this study, laminates were subjected to repeated impact loading up to maximum of 40 impacts at energy levels ranging from 10 to 50 J. Results of repeated impact study are reported in terms of peak load, absorbed energy and projected damage area. All the laminates, sustained repeated impact loading up to 30 J. Beyond 30 J, laminates failed to carry repeated loading beyond certain numbers, which depended on the laminate configuration.