Fatigue and fracture behavior of Nb fiber-reinforced MoSi2 composites

Fatigue and fracture mechanisms in Nb fiber-reinforced MoSi₂ composites are elucidated in this article. The effects of fiber diameter on fracture and crack-tip shielding mechanisms are discussed after a review of micromechanical models which are applied to the prediction of residual stress levels, toughening, and microcracking phenomena. Toughening is shown to occur by a combination of crack bridging and crack-tip blunting under monotonic and cyclic loading. However, the observed failure mechanisms are different under monotonic and cyclic loading. Composites with smaller (250-μm) fiber diameters are shown to have better fatigue resistance and lower fracture toughness than composites with larger (750-μm) fiber diameters. The occurrence of slower fatigue crack growth rates in the composites reinforced with smaller diameter Nb fibers is rationalized by assessing the combined effects of fiber spacing and interfacial crack growth on the average crack growth rates within the composites.