Tension-compression fatigue behavior of 3D woven composites

In order to investigate the fatigue behavior of three-dimensional (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 contains three stages mainly, in which 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 are perpendicular to the loading direction and the fracture of yarn which are along the loading direction are major failure modes. Semi-empirical models are obtained to describe the fatigue process and forecast the fatigue life of 3D woven composites. The mathematical equations fit the experimental results well. (paper)