Failure progress of stitched reinforced polyester - glass laminate at static bending

The course of failure of polyester-glass fabric laminates, classic (non-stitched) and stitched ones (Fig. 1, 2), has been studied at three-point static bending tests of the samples. The failure progress was recorded using photographic (Fig. 3-5) and acoustic emission (Fig. 6-9) methods. It was found that failure process initiation in stitched or non-stitched laminates run by delamination. Delamination in stitched laminates is clearly limited by stitches as the forces causing tangential or translaminar stresses are carried by the stitches to reinforcement layers in a laminate. So the stitched laminate shows milder failure progress than the classic one. At the moment of reaching the maximal stress a dominant failure mechanism in non-stitched composite is delaminating cracking of a matrix while in stitched laminate - cracking of reinforcing fibers. In the latter the higher number of elementary cracks of both components was observed than in classic one, what probably resulted from the higher number of structural defects.