Finite element analyses on three-point low-cyclic bending fatigue of 3-D braided composite materials at microstructure level

Abstract

Abstract This paper presents numerical analyses of fatigue behaviors of three-dimensional (3-D) 4-step rectangular braided composite material under three-point low-cyclic bending. A microstructure model of the 3-D braided composite was established to calculate the bending fatigue deformation and failure with a finite element method (FEM). The stiffness degradation and failure morphologies were obtained from the FEM results and compared with those from experimental. The stress distributions, stress hysteresis and failures of fiber tows and resins at different parts of the 3-D braided composite material have been collected from the FEM calculations to analyze the fatigue failure mechanisms. The influences of the braided preform microstructure on the fatigue damage were discussed. It is found that the surface yarns share more loads than the yarns of the inner part. The stress concentration appeared at the regions with larger changes of fiber tow orientation angles. The fatigue damage evolutions were also used to explain the mechanical behaviors degradation. The crack generation and fatigue damages development of the braided composite appeared at early stages and followed by crack propagation afterwards. A series of damage evolution at the different loading cycles were obtained to unveil the fatigue damage mechanisms. From the investigation, the fatigue resistance of 3-D braided composite could be optimized from improving the mechanical behaviors of surface fiber tows and decreasing the change of fiber tows orientation angles.