Journal of Micromechanics and Molecular Physics

Spark plasma sintering (SPS) of pure commercially sub-micron B₄C powder at 1700–1900${}^{\circ }$C for 20min has been conducted and their wear properties have been investigated by reciprocating friction and wear test. It was found that the relative density increased with the increase and the grain size increased a little at 1700–1900${}^{\circ }$C. Wear mechanisms in the temperature range of 1700–1900${}^{\circ }$C have been proposed such that at 1700${}^{\circ }$C the wear mechanism was dominated by plastic deformation and intergranular fracture, while at 1800–1900${}^{\circ }$C there was transition to the surface fracture or grain pull-out. A model for the spherical abrasive wear was proposed to describe the friction and wear of the B₄C ceramics which is well-fitting with the experimental results.

The interaction of point defects with low-angle (100), (110) and (111) twist boundaries in fcc metals Ni, Cu, Al and role of the point defects in self-diffusion along considered boundaries were studied by the molecular dynamics method. The binding energies of point defects with low-angle twist boundaries were calculated. It was found that the point defects are mainly fixed in the nodes of grain-boundary screw dislocations network. It was shown that the introduced vacancies play an important role in diffusion along twist grain boundaries. The contribution of introduced interstitial atoms to grain-boundary diffusion under thermodynamic equilibrium condition is less by several orders of magnitude in comparison with the contribution of vacancies.

Symmetry-determined nonlinear normal modes, which describe large-amplitude vibrations of diamond lattice, are studied by specific group-theoretical methods. For two of these modes, corresponding to vibrational state with and without multiplication of the unit cell, we present their atomic patterns and dynamical properties obtained with the aid of the ab initio simulations based on the density functional theory (DFT).

In this work, a multiscale cohesive zone model (MCZM) is developed to simulate the high-speed penetration induced dynamic fracture process such as fragmentation in crystalline solids. This model describes bulk material as a local quasi-continuum medium which follows the Cauchy–Born rule while cohesive zone element is governed by an interface depletion potential, such that the cohesive zone constitutive descriptions are genetically consistent with that of bulk element. This multiscale method proved to be effective in describing material inhomogeneities and it is constructed and implemented in a cohesive finite element Galerkin weak formulation. Numerical simulations of high-speed penetration with different shape of penetrators, i.e., square, circle and parabola nose penetrators are performed. Results show that the proposed MCZM can successfully capture spall fracture, the penetration process and different characteristics of fragmentation under different shape of penetrators.

We consider dynamics of a one-dimensional harmonic chain with harmonic on-site potential subjected to kinematic and force loadings. Under kinematic loading, a particle in the chain is displaced according to sinusoidal law. Under force loading, a harmonic force is applied to a particle. Dependence of the total energy supplied to the chain on loading frequency is investigated. Exact and asymptotic expressions for the energy are derived. For loading frequencies inside the spectrum, the energy grows in time. The rate of energy growth depends on the group velocity corresponding to loading frequency. For non-zero group velocities, the energy grows linearly. If the group velocity vanishes, behavior of the system under kinematic and force loadings is qualitatively different. Under kinematic loading, the energy is bounded, while under force loading it grows in time as $t^{\frac{3}{2}}$. Similar problem is solved in continuum formulation for a longitudinally vibrating elastic rod. It is shown that at large times, expressions for energies of the rod and the chain are identical, provided that sound speed and density are chosen properly. Generalization of results for the case of an arbitrary periodic excitation is discussed.