Effect of Temperature on Fracture Toughness of Timetal 834 Titanium Alloy under Mode I and Mixed Mode I/III Loading

The effect of temperature on fracture toughness of Timetal 834 titanium alloy plate under mode I and mixed mode I/III loading was investigated. Both mode I and mixed mode I/III fracture toughness values were initially found to increase as the temperature is increased from room temperature to 723 K. Beyond this temperature, both the fracture toughness values decreased up to 773 K and then showed a significant increase at 823 K. It was also observed that at room temperature, the fracture toughness under mixed mode I/III loading was higher than the corresponding mode I fracture toughness, whereas at 723, 748, and 773 K, the fracture toughness under mixed mode I/III loading was lower than the corresponding mode I fracture toughness, and at 823 K, the two toughness values were comparable. The results were explained on the basis of the occurrence of dynamic strain aging (DSA), change in fracture mechanism, and the nature of the deformation fields ahead of the crack tip under mode I and mixed mode I/III loading.