Research On Fatigue Property Of 2.5 Dimensional Woven Composites

As an important part of composites, 2.5 dimensional woven composites have been widely used in aeronautics, astronautics, medical instruments and so on. Its biggest difference with traditional composite laminates is the lap joint among fibers what results its improvement in inter-laminar property and anti-impact property. In the process of design and use of 2.5D woven composites, fatigue is a key point. As a result, research on the fatigue property of 2.5D woven composites has great significance in theory and engineering.In this article, the micro geometry structure of 2.5D woven composites is analyzed and method of calculating main parameters is defined. And then the unit cell model is built. By the coordinate transformation of local stiffness matrices and the weighed mean of fiber volume content, the whole stiffness matrices can be obtained. Based on this algorithm, a VB program is written to calculate the stiffness. The FEM method is carried on the unit cell, in the given strain and periodic boundary condition, average stress can be obtained to calculate the stiffness by the constitutive formulation. And the results of two methods are compared at last.The whole model is built based on representative volume method. And whether the element fails can be determined by the fatigue failure criterion extended from static failure criterion. So the fatigue process can be simulated by the residual stiffness model and residual strength model based on the damage factor, and an example is given at last.The 2.5D woven composite is comprised of warp layer and weft layer. After the analysis on static loading, the stress redistribution caused by stiffness degradation in the process of fatigue loading is also analyzed. Based on the fatigue life prediction of off-axis unidirectional laminate, a method of predicting the fatigue life of 2.5D woven is proposed by using the Miner theory.All specimen are fabricated by hand lay-up process and RTM. The tests of static strength and fatigue life are carried on. And the test results are compared with the prediction results. The error of the prediction results is less than three times which proves that the accuracy of this method.