Issue 49

A.V. Vakhrushev et alii, Frattura ed Integrità Strutturale, 49 (2019) 370-382; DOI: 10.3221/IGF-ESIS.49.37 376 nanofibers were located in the center of the matrix along the x axis throughout the computational cell. The weight content of the filler was: for nanoparticles 4.23 %, for nanofibers 28.42 %. The use of periodic boundary conditions made it possible to model the deformation and fracture of an “infinite” sample of a nanocomposite formed by the calculation cells along all coordinate axes. x y z (a) (b) Nnanoparticle of Fe Matrix of Al Nanofibre of Fe Matrix of Al Figure 1 : Cross sections of nanocomposite samples with an aluminum matrix and a spherical nanoparticle of aluminum iron (a) and iron nanofibers (b), after relaxation to the deformation stage. After placing the filler (nanoparticles or nanofibers of iron atoms) into a computational cell, which already contains aluminum atoms, the atomic system was relaxed for 20 picoseconds. Relaxation was the restructuring of the atomic system under constant thermodynamic conditions at a temperature of 300 K and the absence of external loads. The temperature was kept constant using the Nose-Hoover thermostat described in detail in article [31]. Relaxation was performed to relieve residual stresses and stabilize the nanosystem. For pure aluminum, the sample was also relaxed for 20 picoseconds under normal thermodynamic conditions. The temperature was also maintained at 300 K. Graphic results for pure aluminum are not shown in Fig. 1, since the structure of the sample did not change during the relaxation process. When modeling the deformation and failure of a nanocomposite, two types of deformation were investigated. In the first case, the sample was subjected to uniform stretching along the x axis; in the second variant, shear strain was studied in the xy plane. The deformation patterns are shown in Fig. 2. x   xy   x y z (a) (b) Figure 2 : Nanocomposite loading scheme for the uniaxial tension (a) and for shear deformation (b). The deformation of the sample was carried out as follows. At each time step, the nanosystem calculation cell changed its geometry. To stretch the nanocomposite, the computational cell expanded along the x axis at a constant speed. For shear deformation, the computational cell changed its geometry, and the original sample in the form of a rectangular parallelepiped turned into a prism. The change in the computational domain is associated with the recalculation of the coordinates of all atoms of the nanosystem. Thus, after cell deformation, all atoms changed their positions in proportion to the magnitude with which the computational domain is modified. After changing the coordinates of the atoms, the forces and velocities of the atoms acting on them were recalculated. In accordance with the current interatomic interaction potentials and the kinetics of motion, the atoms moved in one step in time. The action of the Nose-Hoover thermostat was carried out every 100-1000 time steps of integration. After the finally obtained velocities, coordinates, and forces acting in the atomic system, the parameters of the system were determined: the displacement of atoms of the nanosystem, the stress and strain tensors.