A dislocation density-based CPFE model considering 3D grain morphology on the plastic behaviors of pure titanium

The crystal plasticity finite element (CPFE) method has been widely used to study the effects of grain size and textures on the mechanical behavior of polycrystalline aggregates. To account for grain morphology effects, slip system-dependent characteristic lengths are generally introduced into the slip resistance in crystal plasticity models. However, these characteristic lengths are often determined by approximating grains as ellipsoids and therefore cannot fully capture the complex three-dimensional (3D) morphologies of grains. In this paper, laboratory-based X-ray diffraction contrast tomography (Lab-DCT) was employed to capture 3D grain morphologies of commercially pure titanium (CP-Ti). Geometric models were then directly constructed from the Lab-DCT data. Subsequently, the effects of grain size and morphology were incorporated through a morphology-dependent length into an existing dislocation density-based crystal plasticity constitutive model. This parameter was determined from the effective chord lengths available for dislocation glide on different slip systems. Uniaxial tensile tests and in-situ EBSD tensile tests were conducted to obtain the stress-strain curves and the evolution of the twin volume fraction, which were used to calibrate the constitutive parameters. Various effect mechanism in the proposed constitutive model were further examined using controlled synthetic representative volume elements. In addition, Lab-DCT reconstructed model and statistically equivalent model were simulated to investigate the effects of different statistical descriptors on mechanical responses. This work provides new insights into the role of 3D grain morphology in the mechanical behavior of polycrystalline materials.