On Mechanical Behaviors Of Stitching Composite Materials

As one of the most potential branches of woven composite materials, stitching laminated composite materials has been paid a lot of attention by many researchers in and abroad and been used in a variety of engineering fields due to their simpler technics and lower costs. This paper investigates the mechanical properties of stitching laminated composites by using 3D meso finite element method.It is of most important to select the right boundary conditions when investigating the model of stitching composite materials with meso mechanical method. The traditional assumption of"the plane remains a plane"has been discarded and replaced by a new unified boundary condition to guarantee the continuity of local displacements and stresses on cell boundaries. Four stitching composite materials with different lay-ups have been investigated herein. Comparisons are made between results obtained by using the new boundary condition and available data in the literature. The correctness of the new boundary condition is verified. It is also shown that the present method can be used to predicate elastic properties of stitched laminates effectively. Moreover, the rule of stress distributions within the cell model is given under different loading conditions. It is again verified the conclusion that stitching may reduce the in-plain elasticity properties of laminated composite materials.For a real stitching composite material, two kinds of analytical models, one represent cell model and one full-scale model, are constructed. The problem of interlaminar stress of stitching composite materials is analyzed by using meso finite element method. Thus, the rules of interlaminar stress distributions and the damage of the whole material are obtained. Preliminary experiments are conducted. Base on the experimental data, a new failure criterion of stitching composite materials is proposed.The research is supported by the National Natural Science Foundation of China under contract number of 10472045, and the Aeronautical Science Foundation under contract number of 05B52010.