Equivalent model of stitching reinforcement on composite laminates with a large hole considering fiber damage

Taking into account the effect of the stitching threads on the bending and breaking of the in-plane fibers, the inclusion of stitch holes and resin-rich zones, the research focuses on the stitching reinforcement for the composite laminates containing a large hole (The ratio of laminate's width D and diameter R of the open-hole D/R<6). The finite element simulating calculation was carried out on the stitching reinforcement for composite laminates containing a large circular hole.On the tensile load, the effects of different stitch parameters (stitching needle distance, row spacing, edge distance, diameter and tension) on the mechanical properties of the laminate were calculated. And the damage caused by different stitch parameters to the in-plane fibers is regarded as equivalent to the expansion of the diameter of the hole. The finite element model of the equivalent modal without edge effect laminates was established, and the principle of the influences on the overall mechanical properties of the laminate by different stitch parameters was investigated. The less distance of the stitching needle, the poorer the mechanical properties of the laminates.When the stitching needle distance is less than 3.14 mm, the mechanical properties of the laminate decrease monotonically with the increase of the edge distance. When the stitching needle distance is between 3.14 mm and 6 mm, with the increase of the edge distance, the mechanical properties of the laminate present a trend similar to sine function, and the overall trend is increasing. When the needle distance is more than 6 mm, with the increase of the edge distance, the mechanical properties of the laminates increase monotonically. At the positions of 0° and 90° of the central hole, the defect of the stitch holes causes the early failure of the laminates easily.