Effect of the notch depth on fracture behavior of TC4 titanium alloy sheets

To evaluate the low-stress brittle fracture of TC4 titanium alloy sheet structures, the effect of notch depth (d) on the fracture behavior of the 1.8 mm thick TC4 titanium alloy sheets was investigated combied with tensile tests and digital image correlation method. The results show that the ductile-brittle transition (DBT) occurs with increasing notch depths. Ductile fracture occurs for the notched samples with d = 0.5-1.5 mm, and a uniform plastic deformation stage is observed in the load-displacement (P-L) curves, and there are stretch zone and the stable crack propagation zone in the fracture surfaces. Brittle fracture occurs for the notched samples with d = 3.0-5.0 mm, and there is only the linear elastic stage in the P-L curves, and no stretch zone in the fracture surfaces. The samples at the middle notch depths (d = 2.0-2.5 mm) are in the transition from ductile to brittle fracture, and there exists the elastoplastic deformation stage in the P-L curves, and the stretch zone and stable crack propagation zone are both decreased. The analysis of notch fracture parameters shows that fracture of notched samples is controlled by the stress concentration and the stress field intensity of an imaginary crack with the same notch depth. The effect of crack gradually increases with increasing d, which results in increased brittle fracture tendency. Moreover, the fracture energy gamma f can characterize the DBT of notched TC4 titanium alloy sheets, and the gamma f is proportional to the ratio of critical plastic zone size to d (rpc/d). Finally, the rpc/d is proposed to characterize the DBT of the notched TC4 titanium alloy sheets, and the criterion of the DBT for the notched TC4 titanium alloy sheets is obtained.

Automated summary

The effect of notch depth on the fracture behavior of 1.8 mm thick TC4 titanium alloy sheets was investigated using tensile tests and digital image correlation method. Ductile-brittle transition was observed as the notch depths increased. Ductile fracture occurred for notched samples with a notch depth of 0.5-1.5 mm, while brittle fracture occurred for notch depths of 3.0-5.0 mm. Samples with a notch depth of 2.0-2.5 mm exhibited a transition from ductile to brittle fracture. Fracture energy γf was found to characterize the ductile-brittle transition of notched TC4 titanium alloy sheets.