Simulation of the mechanical response of polycrystalline materials in the Atomsk package

In this work, the deformation behavior of polycrystalline copper with a face-centered cubic lattice under uniaxial tension was investigated using molecular dynamics. Three cubic models measuring 200×200×200A˚, containing 5, 10, and 15 grains, were constructed using the LAMMPS software package. The Atomsk package, employing Voronoi-Dirichlet tessellation to partition the volume into grains, was used as the tool for microstructure generation. The interatomic interaction was described using an embedded atom method (EAM) potential, and the temperature was maintained at 300 K. Loading was applied at a constant strain rate of 1.0 × 10−10, fs−1 along the tensile axis. During the simulation, the components of the stress and strain tensors were computed. Based on these, the stress and strain intensities were determined, and stress-strain diagrams were constructed. It was established that at the initial stage of deformation, the material behavior is linear and corresponds to the elastic regime. Upon reaching a critical strain, a deviation from the linear dependence is observed, associated with the onset of plastic flow. It is shown that an increase in the number of grains leads to a decrease in the maximum achieved stress and an earlier transition to the plastic stage. A comparison of the three models indicates a regular relationship between the mechanical response and the number of grains. The highest stress peak was recorded in the sample containing 5 grains, with the transition to plastic flow occurring at higher strain values. As the number of grains increases to 10 and 15, the maximum stresses decrease, and the deviation from linear elasticity occurs earlier. It was found that an increase in the concentration of grain boundaries, resulting from a larger number of grains, is accompanied by a decrease in the elastic stability limit and an accelerated development of plastic deformations. This finding is in accordance with theoretical concepts of grain boundaries as regions with an increased density of defects, where stress localization and dislocation generation occur