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.