Interface effects on crack deflection and bridging during fatigue crack growth of titanium matrix composites

Abstract

The effect of the interface on the crack deflection and crack bridging behavior of continuous fiber-reinforced titanium matrix composites has been investigated using three interfaces with significantly different mechanical characteristics. Each of these composites exhibited stress ranges in which fiber bridging was present and stress ranges in which stable fiber bridging was not present. The fatigue crack growth rate for all composites, even for the ones that did not exhibit fiber bridging was significantly below that of the matrix. This phenomenon, believed to be an effect of elastic crack shielding, was most significant for composites with the strongest interfacial bond. Interface failure ahead of the crack tip and its influence on the local stress intensity factor is believed to be responsible for the decrease in the shielding effect of low strength interfaces. Interface debonding was observed in all three composites, and damage to the interface ahead of the crack tip was seen in two of the three composites. A stress-based criterion for predicting debonding appeared to effectively explain the crack deflection behavior for the three composites. Evidence of crack deflection even for the strongest interface suggests that there is scope to increase the interface bond strength in SiC/Ti-alloy system for improved transverse properties without compromising the fatigue life.