Suppression of delamination propagation in carbon/epoxy laminates by the use of superelastic stitching wires: preliminary results

摘要

The reinforcement of laminated composites by stitching is a promising technique, especially in the aerospace field. So far the use of Kevlar, glass and carbon yarns as stitching threads has shown great potential in preventing the delamination propagation. In this study, the authors introduced a new stitch system by the use of Shape Memory Alloys (SMA). A superelastic TiNi wire (0.1 mm dia.) was stitched through the thickness of the carbon fibre plies prior to resin infusion. The rectangular 16-layer carbon/epoxy specimens reinforced by superelastic stitches were submitted to a compression-after-impact test (CAI, ASTM D7137). Prior to the compression test, initial delamination was created by low velocity impact testing (ASTM D7136). During the compressive loading, the superelastic stitches were intended to dissipate energy that would otherwise contribute to propagate the existing delamination. The compressive strength of as-impacted SMA-stitched samples was compared to that of Kevlar-stitched and unstitched samples. The results showed that the SMA stitches were effective in reducing the area and volume of the impact-induced delamination, as well as in improving the CAI strength, but the Kevlar stitches were more effective than the TiNi stitches in both tests.