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Studies on Stitched Woven S2 Glass/Epoxy Laminates under Low Velocity and Ballistic Impact Loading

Experimental investigations were carried out to study the response of stitched S2-Glass/SC-15 Epoxy composites under low and ballistic impact loading. Laminates were fabricated using plain weave S2-Glass fabric with SC-15 resin system employing low-cost Vacuum Assisted Resin Infusion Molding (VARIM) process. Both unstitched and stitched laminates were considered. For stitching a 3-cord Kevlar thread was used. Dry fabric preforms were stitched through the thickness to form square grids of size 25.4 and 12.7 mm. Low velocity impact tests were carried out on 5 layer stitched and unstitched laminates of size 90× 90 mm at energy ranging 10-80 J using an instrumented impact testing machine. Transient responses of the laminates were measured and analyzed. For ballistic impact testing, laminates of size 300×300 mm were tested using a gas-gun facility. The panels were impacted using sabot-assisted fragment simulating projectiles. Energy absorbed by the laminates was calculating by measuring inlet and exit velocities. All the samples considered in the study were nondestructively evaluated using ultrasonics for their damage size. Results of the study indicate that stitching considerably enhanced the damage resistance of the laminates by restricting the size of damage as also improving ballistic limits.