PSI - Issue 35

E. Emelianova et al. / Procedia Structural Integrity 35 (2022) 203–209 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Deformation-induced surface roughness is usually considered as an undesired phenomenon that deteriorates the mechanical properties of a material. However, Romanova et al. (2020) have recently demonstrated on the example of polycrystalline titanium that roughening developing at the mesoscale could serve as an early precursor of plastic strain localization. These findings motivated us to continue the investigations for titanium polycrystals to reveal a correlation between the microstructural characteristics, deformation mechanisms, and mesoscale roughness patterns. Generally, roughness characteristics depend on multiple factors, including crystalline structure (Becker, 1998; Wouters et al., 2006), grain size and shape (Mahmudi and Mehdizadeh, 1998; Stoudt and Ricker, 2002; Zhang et al., 2015), crystallographic texture (Becker, 1998; Romanova et al., 2020; Wu et al., 2007), and loading conditions (Wu et al., 2007; Miller, 1987). For the most part, these effects have been investigated on steels and aluminum alloys (see e.g., a review by Li and Fu (2019)), while few studies were reported for hexagonal close packed (hcp) metals. In our recent works (Romanova et al. 2019a, 2020; Emelianova et al., 2020), we examined different aspects of deformation-induced surface roughening in polycrystalline titanium under uniaxial tension, including the influence of surface modification, grain size and grain orientations. It is known that rolled α -titanium is characterized by a basal texture with different misorientation angles between prismatic axes of hcp grains and the normal direction (ND) (Won et al., 2015). It was shown numerically (Romanova et al., 2020) that a basal texture could suppress roughening to a certain extent, although the effects of the texture severity on the roughness patterns were beyond this study. The objective of the present research is to study numerically the effect which the severity of a basal texture has on deformation- induced surface roughening in α titanium subjected to uniaxial tension. The crystal-plasticity finite-element method (CPFEM), along with an explicit integration of a material microstructure in the numerical solution, is proved to be a convenient tool for this kind of research. 2. Microstructure-based model A micromechanical model of polycrystalline α -titanium developed by Emelianova et al. (2021) and Romanova et al. (2019a, 2021) is employed in this study as a tool of numerical investigation. Here we dwell briefly on the key points of the CPFEM simulation procedure. In the framework of microstructure-based simulations, a polycrystal is treated as a conglomerate of grains. Numerically, each grain is represented by a set of finite elements associated with a local frame with the x 1 , x 2 and x 3 axes coinciding with the [101̅ 0] , [1̅ 21̅ 0] and [0001] crystallographic directions (Fig. 1a). The orientations of local (crystal) frames with respect to the global coordinate system with the axes denoted as RD, TD and ND in Fig. 1b are determined through a set of Euler angles.

Fig. 1. Hexagonal close packed (hcp) lattice (a), model grain structure shown in inverse pole figure (IPF) RD colors (b), and schematic representation of a basal texture typical for rolled α -titanium (c).

Based on the experimental data for commercially pure titanium (Kardashev, 2020; Panin et al., 2018; Romanova et al., 2019a), a three-dimensional polycrystalline structure was generated by the method of step-by-step packing