Dina U. Abdullina

This paper presents a study of the electroplastic effect in crystals using the molecular dynamics method.    The main focus is on the selection and comparison of particle interaction potentials when modeling the effect of electric current on the plastic properties of materials.    The aim of the study is to model the dislocation electroplastic effect in crystals using the molecular dynamics method, select optimal particle interaction potentials, and analyze their influence on plastic deformation processes. Copper was chosen as the object of study . In the course of the study, comparative modeling was carried out using the Morse potential and the β-FPUT potential. The effect of an electric current with a density of 108÷109 A/m ² on dislocation mobility and a decrease in the yield strength of the material was studied. It was found that the Morse potential better describes the rupture of bonds at high strains, while β-FPUT more accurately reproduces anharmonic effects at low and medium strains. The modeling results showed that the decrease in activation energy depends linearly on the current density, and the increase in dislocation velocity is exponential. At optimal current density, a decrease in the yield strength of copper by 30÷90 % is observed.    The practical significance of this study lies in determining the optimal current parameters for electroplastic deformation and developing a methodology for selecting interaction potentials when modeling the electroplastic effect. The results obtained can be used to improve metal forming technologies. To improve the accuracy of further research, it is possible to move to three-dimensional models that take into account the actual grain structure, incorporate Joule heating effects, and use multiparticle potentials to better describe the electronic subsystem.

Discrete breathers (DBs) are nonlinear vibrational excitations localized on small groups of atoms in perfect crystal lattices. While theoretically proven, a systematic understanding of DB formation in binary crystals with the B2 structure remains limited. We employ molecular dynamics simulations using the LAMMPS package to investigate the nonlinear dynamics of three representative B2 crystals: ionic CsCl, and intermetallic LiPb and NiTi. We calculate the amplitude-frequency dependencies of delocalized nonlinear vibrational modes (DNVMs) and analyze DB existence conditions based on phonon spectrum features and anharmonicity type. Our analysis reveals that a significant atomic mass difference creates a phonon band gap, enabling gap DBs in CsCl and LiPb, whereas NiTi, with similar atomic masses, exhibits no gap. A simplified model assuming identical bond stiffnesses accurately predicts frequency ratios in CsCl and LiPb but fails for NiTi due to strong bond stiffness asymmetry. We demonstrate the successful excitation of long-lived gap DBs in LiPb by initializing atomic displacements based on the G1 DNVM pattern on heavy Pb atoms. These gap DBs remain stable for over 20 ps with negligible energy dissipation. In contrast, DBs with frequencies above the phonon spectrum (excited on light Li atoms) exhibit shorter lifetimes (~2 ps). The study establishes that both atomic mass ratio and interatomic bond stiffness asymmetry are critical parameters governing nonlinear dynamics in B2 crystals. The predicted long-lived gap DBs in LiPb provide a target for future experimental detection via inelastic neutron or X-ray scattering, offering new insights into energy localization and transport in biatomic alloys.

The electroplastic effect (EPE) is used in metal forming, reducing the forces required to shape metals without significant heating, minimizing tool wear, and producing parts from difficult-to-deform alloys. However, the physical nature of EPE remains insufficiently understood, necessitating fundamental research to uncover the mechanisms of interaction between high-density electric current and a sample. Most EPE studies are conducted by passing an electric current through a sample undergoing plastic deformation, monitoring the movements of the grips, and recording the changes in stresses in the sample. This paper discusses a different deformation scheme, in which a wire sample is loaded with a dead weight and a current pulse is passed through it, causing its plastic deformation. With this deformation scheme, for a sufficiently long sample, Joule heating can be accurately determined from its thermal expansion. This is important for the separation of the thermal and athermal effects influencing electroplastic deformation. The nearly instantaneous heating of a sample when passing a current pulse lasting approximately 10^–4 s results in its thermal expansion, triggering oscillations in the sample-weight system. A condition for the specimen temperature increase, when it appears in a compressed state, is obtained, and Euler critical loads are calculated. For the case where the specimen remains in a stretched state after passing the current pulse, weight oscillations are analyzed for both linear-elastic and elastic-plastic samples. It is shown that, under experimental conditions, the weight oscillation period is significantly longer than the time it takes for a longitudinal sound wave to pass through the specimen, allowing the sample-weight system to be considered a single-degree-of-freedom system. The obtained results demonstrate that experiments studying EPE must take into account the dynamic effects caused by the nearly instantaneous release of Joule heat.

This study investigates the phenomenon of supratransmission in three-dimensional crystals with a B2 (CsCl) structure, employing classical molecular dynamics with β-Fermi–Pasta–Ulam–Tsingou potentials up to fourth-nearest neighbors. We analyze energy transfer from a harmonically driven surface into the crystal bulk across various frequency regimes relative to the phonon spectrum. While low-amplitude excitation results in energy transmission only within the phononic bands, high-amplitude driving triggers supratransmission in the phononic gap and above the optical band. Our results demonstrate that in these nonlinear regimes, energy is transported not by linear phonon waves but by discrete breathers (DBs) emitted quasi-periodically from the surface. A key finding is the distinct sublattice selectivity of these excitations: gap DBs propagate primarily along the heavy atom sublattice, whereas above-spectrum DBs travel along the light atom sublattice. We quantify the velocities and oscillation periods of these localized modes, revealing their critical role in bypassing linear spectral restrictions. These findings provide new insights into nonlinear energy transport in binary alloys and suggest potential applications for controlling heat flow and signal processing in crystals.

A discrete breather (DB) is a spatially localized, large-amplitude vibrational mode in a defect-free nonlinear lattice. The discovery of DBs raised the question of how they can be excited in nonlinear lattices. One possible mechanism is supratransmission, whereby energy is transferred to the lattice from an external source at a frequency outside the phonon spectrum of the lattice. When the amplitude of the external driving is large enough, the DBs are excited and transfer energy to the lattice. In a recent study, we analyzed the supratransmission effect for the β-FPUT square lattice and demonstrated that DBs can be emitted from a pair of periodically driven particles along close-packed directions. The present work demonstrates that DBs can also be excited along the diagonal directions of the lattice. The results confirm the existence of moving DBs propagating either along a close-packed direction or a diagonal direction in the square lattice. This finding is significant because it reveals the mechanisms of energy transport in a square lattice via nonlinear excitations.

Рассматривается биатомныйкристалл со структурой B2 с межатомными взаимодействиями, описываемыми потенциалом β-Ферми-Паста-Улама-Цингу. Анализируется случай большой разницы в атомных массах компонентов, когда в фононном спектре кристалла возникает щель. Пространственно лока-лизованная колебательная мода большой амплитуды, называемая дискретным бризером (ДБ), найдена путем применения функции локализации к делокализованной нелинейной колебательной моде (ДНКМ). ДНКМ и, следовательно, ДБ имеют частоты в щели фононного спектра The biatomic crystal with B2 structure is considered with the interatomic interactions described by the β-Fermi-Pasta-Ulam-Tsingou potential. The case of a large difference in the atomic masses of the components is an-alyzed. The phonon spectrum of the crystal possesses a forbidden zone (gap). A spatially localized large-amplitude vibrational mode, called thediscrete breather (DB), is found by applying a localization function to the delocalized nonlinear vibrational mode (DNVM). The DNVM and consequently the DB have frequencies in the gap of the pho-non spectrum

The article presents several exact solutions of the equations of motion of atoms in a BCC crystal, called delocalized nonlinear vibrational modes (DNVMs). The exact solutions are obtained by analyzing the BCC lattice point symmetry group only, therefore, they exist for any type of interatomic interactions and for any amplitudes. All studied DNVMs are vibrational modes with one degree of freedom. The dependence between frequency and amplitude of DNVMs is calculated using the Fermi-Pasta-Ulam potential with hard type nonlinearity when considering interatomic interactions up to the fourth neighbor. There are seven groups among the 34 studied DNVMs with the same frequency of vibrational modes in the small amplitude limit within each group. This fact is explained by some DNVMs being superpositions of others after applying point symmetry transformations. The obtained results can be to test the interatomic potentials of BCC crystals.

High-density electric current pulses increase the plasticity and reduce the yield stress of metals with negligible heat generation. This effect has great potential for the development of energy-saving technologies for processing hard-to-deform metallic materials. Despite the long history of the study of electroplasticity, there is still no consensus on the physical nature of this effect. In this paper, the effect of repetitive pulses applied at the same or gradually increasing tensile stress on the plastic deformation of copper wire is investigated using a home-made experimental setup. The electroplasticity of the wire in the delivery state and after annealing is compared. It is shown that for a constant tensile stress, the incremental plastic deformation of the wire decreases with each successive pulse. This effect is stronger for annealed wires because they have a lower dislocation density and therefore a lower plasticity resource. The Joule heat release in the specimen and the heating due to plastic deformation are evaluated. The results obtained will be used to fit the parameters of the atomistic model being developed to describe the interaction of electron flow with dislocations.