CRACK BRIDGING IN THE FATIGUE OF FIBROUS COMPOSITES

Abstract— Recent observations of fatigue cracks bridged by continuous fibers in titanium alloy and titanium aluminide composites are compared to analogous observations in fiber-reinforced ceramics under monotonic loading. Three failure modes have been identified under axial loading in each case: longitudinal failure (failure parallel to the fibers) and noncatastrophic and catastrophic mode I failure (failure normal to the fibers). The criteria for transition from one failure mode to another are reviewed. Models developed previously to describe the failure of fiber-reinforced ceramics are extended to describe the mechanics of mode I fatigue crack growth. The extension is straightforward as long as the fibers do not fail in the crack wake, i.e. the failure mode is noncatastrophic mode I failure.