ELASTIC DAMPER BASED ON THE CARBON NANOTUBE BUNDLE

Mechanical response of the carbon nanotube bundle to uniaxial and biaxial lateral compression followed by unloading is modeled under plane strain conditions. The chain model with a reduced number of degrees of freedom is employed with high efficiency. During loading, two critical values of strain are detected. Firstly, period doubling is observed as a result of the second order phase transition, and at higher compressive strain, the first order phase transition takes place when carbon nanotubes start to collapse. The loading-unloading stress-strain curves exhibit a hysteresis loop and, upon unloading, the structure returns to its initial form with no residual strain. This behavior of the nanotube bundle can be employed for the design of an elastic damper

Stable States of Ferroelectric Smectic C* Liquid Crystal Confined between Patterned Surfaces

In this study we consider equilibrium states in a monolayered sample of ferroelectric smectic C∗ confined between two differently patterned substrates with strong anchoring under the applied electric field. By using the continuum theory for a "bookshelf" aligned sample of ferroelectric liquid crystal, we obtain elliptic sine-Gordon equation. It is shown that due to the patterned structure of the substrates, competing boundary conditions in the thin film generate a specific alignment of liquid crystals, which can be controlled by the electric field. This theoretical finding is described as a system with harmonically coupled atoms with an external potential within the framework of the Frenkel-Kontorova model

Frequency voltage controlled light transmittance in ferroelectric liquid crystal cells

Light transmittance of a short-pitch deformed-helix ferroelectric liquid crystal cell was numerically studied when low and high voltage frequencies ($\simeq 1$ kHz and $\simeq 100$ kHz, respectively) are applied to the cell. The reported finding in the decay of light transmittance at increasing frequency is obtained due to reasonable simplifications of the temporal dependence of director's azimuthal angle. By taking experimentally known data, we numerically demonstrate that the increase in temperature of ferroelectric liquid crystals yields an insignificant change of light transmittance within all visible spectra

Partial auxeticity of laterally compressed carbon nanotube bundles

Carbon nanotubes (CNTs) have attracted increasing attention because of their enormous potential in various technologies. Herein, the evolution of the structure and elastic properties of a CNT bundle under compression in uniaxial and biaxial regimes is analyzed using a chain model with a reduced number of degrees of freedom. The compression stress–strain curves consist of four stages, each of which is characterized by a specific structure and deformation mechanism. In the first stage, all CNTs have the same cross section; in the second stage, the translational symmetry is preserved in the system, but with a doubled translational cell; in the third stage, CNT collapse takes place, leading to the loss of the translational symmetry; the fourth stage begins when all CNTs collapse. Elastic constants are calculated for the CNT bundle under uniaxial and biaxial compression during the first two stages. In all loading schemes, during the second stage of deformation, the CNT bundle exhibits partial auxetic properties. The results obtained contribute to the fundamental knowledge for the design of carbon nanomaterials with enhanced properties.Research of E.G.S. was conducted at Tomsk Polytechnic University withinthe framework of Tomsk Polytechnic University CompetitivenessEnhancement Program grant. S.V.D. acknowledges the support of theRussian Science Foundation grant no. 21-19-00813

Discrete breathers in a triangular β-Fermi-Pasta-Ulam-Tsingou lattice

A practical approach to the search for (quasi-) discrete breathers (DBs) in a triangular β-FPUT lattice (after Fermi, Pasta, Ulam, and Tsingou) is proposed. DBs are obtained by superimposing localizing functions on delocalized nonlinear vibrational modes (DNVMs) having frequencies above the phonon spectrum of the lattice. Zero-dimensional and one-dimensional DBs are obtained. The former ones are localized in both spatial dimensions, and the latter ones are only in one dimension. Among the one-dimensional DBs, two families are considered: the first is based on the DNVMs of a triangular lattice, and the second is based on the DNVMs of a chain. We speculate that our systematic approach on the triangular β-FPUT lattice reveals all possible types of spatially localized oscillations with frequencies bifurcating from the upper edge of the phonon band as all DNVMs with frequencies above the phonon band are analyzed.Nanyang Technological UniversityPublished versionThe authors acknowledge the financial support from Nanyang Environment & Water Research Institute. Research of E.G.S. was carried out at National Research Tomsk Polytechnic University within the framework of a Tomsk Polytechnic University Competitiveness Enhancement Program grant

Effect of the stiffness of interparticle bonds on properties of delocalized nonlinear vibrational modes in an fcc lattice

Delocalized nonlinear vibrational modes (DNVMs) supported in crystal lattices are exact solutions to the equations of motion of particles that are determined by the symmetry of the lattices. DNVMs exist for any vibration amplitudes and for any interparticle potentials. It is important to know how the properties of DNVMs depend on the parameters of interparticle potentials. In this work, we analyze the effect of the Morse potential stiffness on the properties of one-component DNVMs in a face-centered cubic (fcc) lattice. In particular, the frequencies, kinetic and potential energy, mechanical stress, and elastic constants of DNVMs in a large range of vibration amplitudes are considered. Frequency-amplitude dependency obtained for the Morse crystal is compared with that obtained earlier for copper by using the potentials of the many-body embedded atom method. The properties of DNVMs are mainly dictated by their symmetry and are less influenced by the interparticle potentials. It is revealed that at low and high stiffness of interparticle bonds, different sets of DNVMs have frequencies above the phonon band. This is important to predict the possible types of discrete breathers supported by the fcc lattice. The results obtained in the work enrich the understanding of the influence of interparticle potentials on the properties of the studied family of exact dynamic solutions.Published versionThe work of S.S. (derivation of DNVMs) and S.D. (discussion, writing the manuscript) is funded by the Russian Science Foundation (Grant Reference No. 21-12-00229). E.K. (discussion of the results) is grateful for the financial support of Council on Grants of the President of the Russian Federation (Grant Reference No. NSh 4320.2022.1.2). The work is also supported by the Ministry of Science and Higher Education of the Russian Federation within the framework of the state assignment of Ufa State Aviation Technical University, the youth research laboratory ”Metals and Alloys under Extreme Impacts” (Agreement No. 075-03-2022-318/1)