三维机织复合材料在拉压循环载荷下的疲劳性能

为研究三维机织复合材料在拉伸-压缩循环载荷下的疲劳性能，对材料进行了应力比R=-1的疲劳试验。在不同的载荷水平下，分别进行了纬向和经向两类拉压疲劳试验。试验获得了试样在疲劳载荷下的滞回曲线和全过程中剩余刚度比随寿命的变化曲线。结果表明，在拉伸-压缩循环载荷下，三维机织复合材料的疲劳损伤过程主要包含3个阶段，分别发生基体破坏、纱线横向裂纹扩展和纱线的最终断裂。基体的破碎和开胶、垂直于载荷方向排布的纱线撕裂和沿载荷方向排布的纱线断裂是试样内部的主要失效模式。试验还获得了纬向和经向拉压疲劳的拟合S-N曲线，可应用于工程中对该型材料进行疲劳寿命估算。该型材料的疲劳寿命在低应力区和高应力区均显示出较小的分散性，双对数坐标系下的拟合S-N曲线具有较好的线性度。

Fatigue behaviors of 3D woven composites under tension-compression cyclic loading

In order to investigate the fatigue behaviors of 3D woven composites under tension-compression cyclic loading, fatigue tests which had a stress ratio of R=-1 were conducted. Under different loading levels, weft and warp fatigue tests were conducted. The hysteresis loops and curves of residual stiffness ratio via fatigue life were obtained. It is implicated that the fatigued damage progress of 3D woven composites under tension-compression cyclic loading mainly contains three stages:the failure of matrix, transverse crack propagation inside the yarns and the fracture of yarns occur in sequence. The crush and debonding of matrix, the avulsion of yarns which is perpendicular to the loading direction and the fracture of yarn which is along the loading direction are major failure modes. The fitted tension-compression fatigue S-N curves were also obtained, which can be applied in engineering to estimate fatigue life of this type of material. Both fatigue life in low and high stress region show small variance. The fitting S-N curves have good linearity in the double logarithm coordinate.