Experimental investigation of three-dimensional mixed-mode fracture of a titanium alloy at room and elevated temperatures

Damage tolerance of titanium alloy structures is very important for the safety of modern aircraft under complex loading and environmental conditions. However, there is no available systematic knowledge about the effect of alloy thickness under mixed-mode loading at elevated temperatures. In the present study, a newly developed fracture experimental technique based on high-temperature moiré interferometry was employed to investigate experimentally I-II mixed-mode fracture in titanium alloy TC11 of various thicknesses at room and elevated temperatures. Compact shear specimens with thickness ranging from 1.8 to 7.1 mm were tested. The effects of temperature, thickness, and loading angle on the load capacity and crack initiation angle were investigated systematically. The TC11 alloy was shown to possess varied fracture performance at elevated temperature, and an opposite thickness effect at room temperature. Increasing temperature would enhance the fracture load capacity of thick specimens but reduce the fracture load capacity of thin specimens. Crack initiation angles under I-II mixed-mode loading showed the thickness-temperature coupling effects. These complex effects call for new development in three-dimensional mixed-mode fracture theory and technologies for damage tolerance assessment.