Identification of Post-necking Strain Hardening Behavior of Pure Titanium Sheet

Abstract

This paper deals with the identification of the post-necking strain hardening behavior of pure titanium sheet. Biaxial tensile tests using a servo-controlled multi-axial tube expansion testing machine revealed that commercial pure titanium sheet exhibits significant differential work hardening (DWH). The latter phenomenon implies that the shapes of the work contours significantly change during plastic deformation which is accurately measured in the first quadrant of the stress space up to an equivalent plastic strain of approximately 0.3. In this paper we focus on the plastic material behavior beyond the point of maximum uniform strain in a quasi-static tensile test. To this purpose, the material is subjected to a post-necking tensile experiment during which the strain field in the diffuse necking zone is measured using a dedicated Digital Image Correlation (DIC) system. The key point in the identification of the post-necking strain hardening is the minimization of the discrepancy between the external work and internal work in the necking zone. In this study, we scrutinize the influence of DWH in the pre-necking regime on the identification of the post-necking strain hardening behavior of pure titanium sheet. Finally, a strain hardening model which enables disentangling pre- and post-necking hardening behavior is presented.