Micromechanics modeling of fatigue hysteresis loops in carbon fiber-reinforced ceramic-matrix composites

When fiber-reinforced ceramic-matrix composites (CMCs) are first loading to fatigue peak stress, matrix multicracking and fiber/matrix interface debonding occur. Under fatigue loading, the stress–strain hysteresis loops appear as the frictional slip occurred between the fiber and the matrix in the interface debonded region. The micromechanics fatigue hysteresis loops models of fiber-reinforced CMCs have been developed for different fiber preforms, i.e., unidirectional, cross-ply, and woven CMCs. The interface slip lengths, i.e., the interface debonded length upon first loading, unloading interface counter slip length, and reloading interface new slip length, were determined by fracture mechanics approach. The fatigue hysteresis loops of different interface debonding and slipping cases have been analyzed. The fatigue hysteresis loss energy is formulated in terms of fiber/matrix interface shear stress in the interface debonded region. When the interface shear stress decreases, the fatigue hysteresis loss energy first increases to the maximum value and then decreases to zero. By assuming the mechanical hysteresis behavior of cross-ply and woven CMCs was mainly controlled by interface frictional slip in the 0° plies or longitudinal yarns, considering the effect of matrix multicracking modes in cross-ply or woven CMCs, the fatigue hysteresis loops of fiber-reinforced CMCs with different fiber preforms under different peak stresses corresponding to different number of applied cycles have been predicted.