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The effect of external dry friction on the stress-strain state of a semi-infinite elastoplastic rod under sudden loading is under study. It is assumed that the behavior of the rod is described by the Prandtl model, and friction with the environment moving at a constant velocity occurs according to the Coulomb law with different values of the friction coefficient in the perturbed and unperturbed regions of the rod. Analytical solutions are obtained. The conditions under which the rod is an elastic body in a region (part of it) between the fronts of plastic and elastic waves are determined.

The effect of non-conducting extended inclusions (cracks) on the electrical conductivity of a conductive medium at direct current was studied using a two-dimensional model. The additional electrical resistance due to the presence of cracks was calculated using the hydrodynamic analogy between potential flow of an ideal incompressible fluid around solids and electric current flowing around cracks. The dependences of the relative additional electrical resistance of the material on the fracturing coefficient in various limiting cases were determined. Their correctness is confirmed by the results of numerical analysis of the obtained expressions for various fracturing coefficients of the sample for thin and thick samples. The cases of parallel cracks and cracks randomly oriented in different directions were investigated.

This paper presents a study of the thermal and thermally stressed state of a reactor in the form of a quartz cylinder filled with tin for producing hydrogen by methane pyrolysis. When determining the temperature state, the problem for the two-layer structure (quartz-tin) using the Heaviside function was reduced to the problem for a single-layer structure with variable (piecewise homogeneous) properties of the material. An analytical solution including algebraic polynomial functions with coefficients exponentially stabilizing in time was obtained by determining the position of the temperature disturbance front and additional boundary conditions using the integral method of heat balance. Using the obtained solution, quasi-static temperature stresses were determined in the case where the structure is a two-layer hollow cylinder (flat deformation). The layer conjugation method was used to obtain an exact analytical solution of the thermoelasticity problem, from which it follows that at the point of contact of the layers, the hoop and axial stresses have a jump (discontinuity) with a change of sign in it. It is found that in certain start-up modes, the hoop and axial stresses can exceed the tensile strength of the quartz layer. The results were used to determine start-up modes in which the stresses do not exceed permissible values.

Based on the nonlocal strain gradient theory, the transverse vibration of a viscoelastic graphene sheet subjected to an in-plane magnetic field and external forces is studied. A general governing equation for the graphene sheet vibration is formulated. Theoretical solutions for undamped and damped vibrational frequencies are obtained. The influence of the in-plane magnetic field on the damping ratio and on the frequencies of the free and forced vibrations is studied within the framework of the nonlocal strain gradient theory.

Nonlinear parametric oscillations of a longitudinally reinforced orthotropic cylindrical shell filled with a viscous liquid are studied. Fluid motion is described using a linearized Navier-Stokes equation. Equations of motion for a reinforced orthotropic shell filled with viscous liquid are obtained based on the Ostrogradsky-Hamilton principle of stationary action. The dependences of the ratio of the nonlinear frequency to the linear frequency on the deflection of the shell are determined for different numbers of reinforcing ribs.

In this paper, a progressive damage analysis of two-dimensional C/SiC composites and superalloy mechanically fastened joint with a countersunk bolt is implemented to simulate the uniaxial tensile loading process by using a user-defined subroutine UMAT embedded into the general package ABAQUS. On the basis of the developed damage model, a parametric study is carried out to illustrate the effects of countersunk parameters on tensile performance for the hybrid bolted joint. It is found that there are negligible changes in the stiffness of the bolted joint, as the countersunk height varies from 1.5 to 2.5 mm for the considered bolt-head diameter cases. However, the failure load of the ceramic matrix composite and superalloy hybrid joint exhibits significant changes under different combinations of countersunk parameters. Increasing the countersunk height of the bolt intensifies the initial stress concentration and results in the redistribution of stress around the hole-edge area of the composite material plate. For the bolt-head diameter and countersunk height equal to 9.4 and 1.5 mm, respectively, the joint structure ensures the maximum load-bearing capacity for the studied joint with a countersunk bolt.

Results of numerical simulations of reacting turbulent flows in a channel with a rectangular cross section and sudden expansion (backward-facing step) are reported. The simulations are performed for test conditions in a high-enthalpy hotshot wind tunnel with the Mach number at the channel entrance M = 3.85. Hydrogen is used as a fuel; it is injected transversely to the main flow ahead of the step from the upper and lower walls of the channel. The computations are performed in an unsteady three-dimensional formulation with the use of the Fluent 2020R1 software with reactions of hydrogen combustion in air being ignored or taken into account. The structure of reacting turbulent flows is studied; the flow parameters at different stages of the unsteady process of ignition and flame stabilization are determined. The computed data are compared with the results of an experiment in which the static pressure distribution over the channel walls were measured. It is demonstrated that the simulations correctly predict the unsteady pattern of ignition and flame propagation along the channel.

To reveal the influence of vent parameters on the dynamic mechanism of an external explosion induced by a vented premixed methane-air explosion, the evolution process of an outdoor flow field under different vent opening pressures ( p_v ), opening times ( t_v ), and scaled vent size ( K_v = A_v / V ^2/3) is studied by methods of computational fluid dynamics. With an increase in K_v , the shape of the unburned gas cloud and vented flame gradually changes from a jet shape to a depression toward the vent. The outdoor peak specific turbulent kinetic energy increases by 36.5 and 4 times with an increase in p_v and t_v , respectively. At t_v = 0.1 s, the peak specific turbulent kinetic energy reaches 1 411 m²/s² and the turbulence range reaches 3 times the length of the room. With an increase in p_v , t_v , and K_v , the occurrence time interval of the external explosion exhibits a decreasing trend. The external explosion is located at a distance of less than 1.4 times the length of the room. At K_v = 0.05, the external explosion occurs at the furthest location.

Regimes of continuous multifront detonation in a methane mixture with heated air in a flow-type annular combustor 503 mm in diameter are obtained and studied for the first time. Air is preheated by straight firing from 600 to 1 200 K in the settling chamber by means of burning a stoichiometric hydrogen-oxygen mixture entering the combustor; the air flow rate is 6 ÷ 20.9 kg/s. The fuel (methane)-to-air equivalence ratio is 1.15 ± 0.1. The influence of the air heating level on the domain of continuous detonation, pressure in the combustor, and specific impulse is analyzed. Regimes of continuous multifront detonation with one pair of colliding transverse waves with a frequency of 1.2 ± 0.1 kHz are observed in all experiments at air temperatures ranging from 600 to 1 200 K. Based on the stagnation pressures measured at the combustor exit, the specific impulse of continuous detonation is determined as a function of the air flow rate and its temperature. As the air heating temperature increases, the specific impulse of the thrust force is found to decrease owing to the increase in the degree of dissociation of the detonation products. The maximum specific impulse with allowance for the heated air energy, equal to 1 630 s, is obtained for the air temperature in the settling chamber equal to 600 K.

The use of nanosized metal powders is a promising direction in the development of modern energy compositions due to their high reactivity and intense heat release upon contact with an oxidizer and during combustion. The results of a combined TG-DSC analysis of Alex aluminum nanopowders and a Al-Cu compound, obtained via electrical explosion of conductors, are presented at constant heating rates of 2, 4, and 20 °С/min in air in a temperature range of 30 ÷ 1 300 °С. It is revealed that Alex and Al-Cu nanopowders are intensely oxidized when heated in air to a temperature of 600 °С due to the oxidizer diffusion through the porous oxide layer Al₂O₃ and the possible formation of open surfaces of an active metal during a phase change in the crystal lattice of the metal oxide. The Friedman and Kissinger-Akahira-Sunose (KAS) methods were used to obtain dependences between the activation oxidation energy on the degree of conversion (oxidation) of nanosized metal powders. It is shown that the activation energy of Alex and Al-Cu nanopowders depends on the degree of conversion (oxidation stages) and lies in ranges of 78 ÷ 307 and 99 ÷ 430 kJ/mol, respectively.