Statistical model of the 3-D braided composites strength

Abstract

Abstract： Based on the statistical model for the tensile statistical strength of unidirectional composite materials and the stress analysis of 3-D braided composites, a new method is proposed to calculate the tensile statistical strength of the 3-D braided composites. With this method, the strength of 3-D braided composites can be calculated with very large accuracy, and the statistical parameters of 3-D braided composites can be determined. The numerical result shows that the tensile statistical strength of 3-D braided composites can be predicted using this method. Some researches have been reported [1] about stiffness and elastic constant of 3-D braided composites. Compared with the stiffness problem, strength problem of 3-D braided composites is more complex. There are two main reasons: firstly, the global properties of 3-D braided composite are more complicated than laminates, so these methods are not adopted directly to 3-D braided composites; secondly, the strength of composites is a complex statistical mechanics problem concerning situ characteristic, synergism effect, lamination effect, random bug, etc [2,3] , so that the traditional strength theory is very difficult to be adopted to composites. In order to satisfactorily analyze the failure and damage of 3-D braided composites, it is necessary to adopt statistical micro-mechanics to overcome the drawback of traditional strength theory.The structure of 3-D braided composites is a unitary three-directional space structure composed of interlacing fibers. Fibers and matrix materials of 3-D braided composites are tightly kinky unlike unidirectional composites and cross-ply laminates with the obvious interface effect between fiber and matrix. According to the fatigue test of 3-D braided composites by Tang et al [4] , in the course of the damage of 3-D braided composites, the damage of fiber and bundle is the principal effect. This shows the different failure models between 3-D braided composites and laminates, so the strength prediction methods based on the random critical-core probability model about unidirectional composites and cross-ply laminates can not be adapted to 3-D braided composites. Up to now, there is no report about the statistical strength analysis of 3-D