Unusual plastic deformation and damage features in Titanium: experimental tests and constitutive modeling

In this paper, we present an experimental study on plastic deformation and damage of polycrystalline pure Ti, as well as modeling of the observed behavior. From the mechanical characterization data, it can be concluded that the material displays anisotropy and tension-compression asymmetry. As concerns damage, the X-ray tomography measurements conducted reveal that damage distribution and evolution in this HCP Ti material is markedly different than in a typical FCC material such as copper. Stewart and Cazacu (2011) anisotropic elastic/plastic damage model is used to describe the behavior. All material parameters involved in this model have a clear physical significance, being related to plastic properties, and are determined based on very few simple mechanical tests. It is shown that this model predicts correctly the anisotropy in plastic deformation, and its strong influence on damage distribution and damage accumulation in Ti. Specifically, for a smooth axisymmetric specimen subject to uniaxial tension, damage initiates at the center of the specimen and is diffuse; the level of damage close to failure is very low. On the other hand, for a notched specimen subject to the same loading, the model predicts that damage initiates at the outer surface of the specimen, and further grows from the outer surface to the center of the specimen, which corroborates with the in-situ tomography data.