Multi-Needle Stitching/Tufting Of Sandwich Composites For Improved Damage Tolerance

摘要

The aim of this study is to investigate the damage tolerance of foam core sandwich composites by stitch-bonding. Stitch-bonding is a cost-effective technique and it involves the insertion of high tensile strength yarn through an uncured structure by a stitching machine. However, stitch-bonding of hard/rigid close-cellular foam core based sandwich composites can not be achieved by the available textile processes.A novel multi-needle orthogonal (90°) and bias (45 °) stitch-bonding machine on the basis of the modified lock stitching technique has been developed for foam core sandwich composites. A row of needles penetrate through the PVC foam core sandwich panels with woven carbon skins and the stitching yarns are locked on the other side of the sandwich panels by means of a rapier mechanism. Yarns are fed from a yarn creel. Alternatively, tufting insertion of a loop thread without a lock thread can be employed.The structural performance of stitch-bonded sandwich panels impregnated with epoxy resin in a vacuum-bagging process has been explored. Quasi-static indentation and three-point bending tests were conducted on unstitched and stitch-bonded samples. Stitch-bonded sandwich panels showed localised damage during quasi-static indentation tests, thus showing a great potential for damage tolerance and repair. According to the three point bending test results, the bending stiffness increased with the existense of the stitches and it was higher for the bias stitches.