Interfacial Failure in Stitched Foam Sandwich Composites

In this paper, the use of a customized automatic reinforcement stitching equipment was demonstrated. The stitching of foam sandwich composite preforms was achieved to obtain structures with improved interfacial properties. The effect of different stitching spacings on the crack propagation process in glass fiber reinforced plastics (GFRP)/foam sandwich composite interfaces was examined by Mode-I Cracked Sandwich Beam (CSB) fracture tests. The load–displacement curve, the crack propagation process, and the release rate of critical strain energy were analyzed. The CSB fracture test results show that the stitching treatment with different stitching spacings increase the peak load and fracture displacement. Furthermore, it was found that the mechanism of crack propagation is changed by the stitching process. The release rates of the critical strain energy in specimens with 0- and 10-mm stitch spacings were evenly distributed, with an average of 0.961 kJ/m2 and 1.667 kJ/m2, respectively, while the release rates of critical strain energy in specimens with 6-mm and 8-mm stitch spacings were linearly distributed. The CSB fracture tests confirmed that the best suture spacing was 8 mm. Based on these results, the mechanism of crack propagation and the toughening mechanism of the resin column could be revealed.