Characterization and modeling of anisotropic damage evolution for large-diameter thin-walled CP-Ti tube

Tubular titanium components have been widely used in advanced equipment in aerospace, marine, energy, and healthcare fields over the past decades. For commercial pure titanium (CP-Ti) tubes with hexagonal close-packed (HCP) crystal structure, the limited slip systems and the strong texture caused by multi-pass thermal–mechanical processing make the material always exhibit a strong anisotropy in damage evolution, which easily leads to early failure of components during forming processes. The accurate characterization and modeling of anisotropic damage evolution is a non-trivial issue for excavating the forming potential of materials. In this study, firstly, by taking the large-diameter thin-walled CP-Ti tube as a case material, the uniaxial tension tests along the 0°, 45°, and 90° directions, as well as the simple shear and plane strain tension tests, were designed and conducted to obtain the anisotropic plasticity and fracture behaviors. Then, by integrating a direction-dependent damage rate multiplier and the Hill'48 yield function into the Lode-parameter dependent Lemaitre (Lode-Lemaitre) damage model, the modified Lode-Lemaitre model was established, numerically implemented, and calibrated for the description of the anisotropic damage evolution of the CP-Ti tube. Finally, the prediction ability of the modified Lode-Lemaitre model was evaluated, and the damage evolution of the CP-Ti tube under various loading conditions was analyzed. The comparisons of the experimental and simulation results show that the prediction error of fracture displacement was reduced from 43.2% to 5.48%, and the wall thickness distribution of the Y-shaped tube was accurately predicted. These results prove that the modified Lode-Lemaitre model can accurately describe the anisotropic damage evolution of the CP-Ti tube.