Mode I Interlaminar Fracture Toughness of Stitched Laminates

A stitch method was adopted to improve interlaminar fracture toughness of fabric-reinforced laminates. The double cantilever beam (DCB) test was executed for stitched laminates to study interlaminar fracture toughness and fracture behaviour. The improved insert type loading fixture was adopted to test the Mode I interlaminar fracture toughness (GIC) of different stitching laminates and the relation between the stitch parameters (stitch density) and the interlaminar fracture toughness (GIC) was discussed. In order to improve the average interlaminar fracture toughness, stitching technique was optimized under the restriction of stretching and curving strength. Photographic microscope was used to observe the fracture interface. The effect of stitching parameters on the other performance was also analyzed. The results show that the test of the interlaminar fracture toughness of the laminate can be easily done by using the improved insert type loading fixture; The extension of the opening is discontinuous and the stitch density has a great effect on the opening extension; The bigger the stitch density is, the bigger the interlaminar fracture toughness is, but the stretching and curving strengths decrease with the increasing of the stitch density, and the stitch density has a optimum value.