| Summary: | 碩士 === 逢甲大學 === 機械工程學系 === 87 === For many decades, composite materials have been gained extensive use from commercial, military to aircraft applications due to their excellent performance characteristics, high strength to weight and high stiffness to weight ratios. However , because of the inherent weakness of the matrix in a laminate, damages may occur by manufacturing defects or service usage causing matrix cracking, delamination, fiber breakage and debonding. Along with the possible failure modes, delamination represents the serious one in laminated composite structures. Owing to the mismatch in mechanical properties between plies, the composite laminated plate containing a hole subjected to in-plane loading develops high interlaminar stresses in the boundary layer regions close to the free edge or around the hole.
In this paper, a progressive delamination model based on the three-dimensional eight-node hybrid stress finite element and quadratic delamination criterion is presented for the laminated composite plate containing a central hole subjected to uniform tensile load. The model is capable of predicting the delamination onset strength and of assessing its growth with arbitrary ply-orientations of notched laminates. The model consists of two parts, the interlaminar stress distributions and the delamination growth analysis. The interlaminar stresses in laminates were evaluated by hybrid finite element method, whereas the delamination accumulation in laminates was analyzed by the quadratic delamination criterion combined with a proposed property degradation model. From the stress analysis, it was found high gradient variation in stresses appeared on the straight free edge and around the hole, thus laying down the course of delamination extension. It was revealed from growth survey that the smaller angle between two adjacent plies as well as angles between the two plies orientations and the parallel to load will provide greater prevention to delamination growth.
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