Mechanical behavior of CP-Ti at high strain rates and under stress triaxiality

Abstract

In this study, we investigated the influence of stress triaxiality on the mechanical behavior of commercially pure (CP-Ti) VT1-0 titanium (Grade 2) in the range of strain rates from 0.1 to 103 s−1. Tensile tests were carried out on flat notched and smooth specimens using an Instron VHS 40 / 50–20 servo-hydraulic testing machine. Phantom V711 was used to capture the deformation process of the specimens. The digital image correlation (DIC) method was employed to investigate the evolution of local fields in the gauge section of the specimen. Fracture surface topology analysis was performed using the Keyence VHX‐600D digital microscope. The results revealed that an increase in the strain rate from 102 to 103 s−1 leads to a significant discrepancy between the relative residual elongation δ and the strains that occur in the localization bands prior to crack initiation. CP-Ti undergoes fracture due to nucleation, growth, and coalescence of damage in bands of localized plastic deformation oriented along the maximum shear stresses. Fracture surface analysis indicated an increase in the surface roughness parameter with increasing stress triaxiality. The results confirm that the fracture of commercially pure titanium exhibits ductile behavior at strain rates from 0.1 to 103 s−1, for triaxiality stress parameter 0.333 ≤ η < 0.5, and at a temperature close to 295 K. The least influence of stress triaxiality on the strain-to-fracture appeared at a strain rate of 103 s−1.