Springback nonlinearity of high-strength titanium alloy tube upon mandrel bending

Taking the stress-relieved Ti-3Al-2. 5V tube as the objective, regarding both angular and radius springback, the nonlinear springback behaviors of the high-strength titanium tube (HSTT) upon the universal bending, viz., mandrel bending (rotary draw bending), areclarified. The experiments are conducted to identify the springback and validate the theoretical models, and the deformation theory of plasticity and the explicit/implicit 3D-FE based models are used to reveal the rules and the physical mechanism of the nonlinearity of elastic recovery. The results show that: 1) At early bending stages, the angular springback increases nonlinearly with larger bending angles, then it increases linearly when the bending angle exceeds a critical one; While the radius growth decreases exponentially with the increasing of the bending angles at early stages, then it remains unchanged when the bending angle exceeds another critical value; The springback behaves more nonlinearly under smaller bending radii; Both the critical values for the two springback phenomena become larger with smaller bending radii; The critical angle for radius springback is larger than the one for angular springback. 2) The relationship between the radius springback and angular one is further identified; The radius springback can be estimated by the angular springback of the bending regions of tube; The variation of bending radii has significant effect on angular and radius springback, while it has little influence on the springback angle by the straight regions; The variation of the material properties affects both the springback phenomena much more significantly than the changing of the processing parameters.