Issue 49

A.V. Vakhrushev et alii, Frattura ed Integrità Strutturale, 49 (2019) 370-382; DOI: 10.3221/IGF-ESIS.49.37 377 Let us consider in detail the picture of the deformation and failure of the material in the process of stretching and shear deformation. The deformation processes of tension and failure of the specimen from pure aluminum and nanocomposites under study are shown in Figs. 3, 4 and 5, respectively. Tension patterns are presented for various moments of modeling. x y z a) с) b) A B Figure 3 : Pure aluminum sample tensile strain for simulation time of 5 psec (deformation 0.05) a; 33 psec (deformation 0.33) b; 80 psec (deformation 0.80) c. The images in Fig. 3 illustrate the stretching of pure aluminum. Note that, within a small strain along the x -axis to 0.05, the structure of the material remains almost unchanged (Fig. 3 a). Then, as deformation increases, an active restructuring of the atomic structure of the material follows. Atoms are displaced relative to the lattice sites (Fig. 3 b). In the structure of the material formed areas of defects (dislocations). Fig. 3 b, corresponding to a strain of 0.33, shows an example of such a region (B). In it, the symmetry of the coordinate positions of atoms is broken and new forms of equilibrium of atomic structure appear. At the same time, the crystallite regions (A) are preserved in the material. Further, with an increase in the deformation to 0.8 (Fig. 3 c), the area with defects fills the entire volume of the sample, its stretching is observed, the cross section decreases. Full rupture and failure at this stage does not occur, but the crystal structure of the material is completely transformed into amorphous. The introduction of iron nanoparticles into the aluminum matrix dramatically changes the processes of deformation and failure of the material under tension. The patterns of deformation and rupture of a material with a nanoparticle are shown in Fig. 4. With small deformations along the x -axis to 0.05, the structure of the material remains almost unchanged (Fig. 4 a) as in pure aluminum. Then, as the strain increases to 0.2, a substantial rearrangement of the crystal lattice of aluminum atoms is observed (Fig. 4 b) only in the contact area of the matrix and the filler. The aluminum crystal lattice is distorted, and defects are formed in it. At the same time, the iron atoms forming the nanoparticle change their coordinates insignificantly, therefore the atomic structure of the nanoparticle remains almost unchanged. This is due to the stronger potential of interaction between iron atoms than between aluminum atoms. Note that the structure of the aluminum matrix that is not in contact with the nanoparticle remains unchanged. The failure of an aluminum nanocomposite with an iron nanoparticle begins directly in the region of contact between the iron nanoparticle and the aluminum matrix as a result of the detachment of the aluminum matrix from the nanoparticle surface and subsequent rupture of the material (Fig. 4 c). Patterns of the nanocomposite structure with spherical inclusions shown in Fig. 4 b) and Fig. 4 с) correspond to different stages of failure. Fig. 4 b) illustrates the beginning of the process of irreversible deformation. The simulation was carried out using the molecular dynamics apparatus; therefore, any macroscopic criterion for describing the failure of a nanocomposite, the process of which is shown in Fig. 4 b) and Fig. 4 с), in the work was not used. In this case, the failure of the material determines the parameters of the potential of interaction of the atoms forming the nanocomposite. The failure of a nanocomposite occurs when atoms are removed to a distance at which the force of their interaction is zero. In the process loaded with an increasing number of atoms cease to interact with each other, forming separate local areas of failure, which with increasing lead to the complete destruction of the simulated material. The deformation and failure of a nanocomposite with an aluminum matrix and an iron nanofiber for different levels of deformation is shown in Fig. 5. As in previous cases, with small deformations along the x -axis up to 0.05, the structure of the matrix material and fiber practically does not change (Fig. 5 a). Then, as the strain increases to 0.2, a substantial rearrangement of the crystal lattice is observed in a matrix of aluminum atoms and in some regions of the iron lattice (Fig.