Micromechanical modeling of fatigue hysteresis behavior in carbon fiber-reinforced ceramic–matrix composites. Part I: Theoretical analysis

Abstract

Under fatigue loading of fiber-reinforced ceramic–matrix composites (CMCs), fiber slipping relative to matrix in the interface debonded region upon unloading/reloading is the mainly fatigue damage mechanism. The shape, location and area of fatigue hysteresis loops would change with degradation of the interface shear stress for interface wear or interface oxidation. Based on the fatigue damage mechanism of interface frictional slip between fiber and matrix, the micromechanics fatigue hysteresis loops models corresponding to four different interface slip cases have been developed, in which the unloading interface counter-slip length and reloading interface new-slip length were determined by fracture mechanics approach. The fatigue hysteresis loss energy, fatigue hysteresis loops and interface slip of unidirectional, cross-ply and woven CMCs are formulated in terms of the interface shear stress. With decrease of the interface shear stress, the fatigue hysteresis loss energy increases to the maximum value first, and then decreases to 0; the fatigue hysteresis loops correspond to different interface slip cases. The effects of the fiber volume fraction, fatigue peak stress, fatigue stress amplitude, matrix crack spacing and matrix cracking mode on the fatigue hysteresis loss energy evolution with decrease of the interface shear stress have been analyzed. The range and extent of the interface frictional slip between fiber and matrix during fatigue loading would be decreased with increase of the fiber volume fraction and matrix crack spacing, increased with increase of the fatigue peak stress and fatigue stress amplitude, and greatly affected by matrix cracking mode in cross-ply CMCs.