Mechanics of Solids最新文献

A stochastic model of the wear process of a shaft lip seal that takes into account random changes in the temperature and external load is described. The results of a numerical analysis of the process of seal wear in relation to the conditions of operation in open space at near-Earth orbital stations are presented. The importance of taking into account random changes in temperature and external load for predicting the seal durability is evaluated.

The principle of modifying the mechanical properties of thin-film membrane structures of arbitrary shape by a non-contact method was proposed, implemented and explained for the first time. The idea was tested on a thin-film aluminum membrane formed by the magnetron method on a silicon substrate. The external influence was carried out through a cyclic load in the form of releasing and supplying excess air pressure to the membrane. As a result of repeated impacts, the physical properties of materials (grain size and roughness) and mechanical properties (internal mechanical stresses and critical overpressure) change. Changing the magnitude of residual mechanical stresses in the membrane material allows the formation of a surface with the required curvature value. In this work, after a cyclic load with a pressure equal to half the critical pressure, the following effects were revealed: the deflection of the membrane in the absence of external influence increased by more than an order of magnitude, the structure passed into a plastic type of deformation, the critical burst pressure decreased by several tens of percent. The use of this methodology makes it possible to create new materials with unique mechanical properties.

The review presents systematization and analysis of experimental data on nanoindentation (NI) of a whole class of new materials, namely, wide-gap AlN, GaN, AlGaN, and β-Ga₂O₃ heterostructures formed on a hybrid substrate of a new SiC/Si type, which were synthesized by the method of coordinated atom substitution. The deformational and mechanical properties of the investigated materials are described in detail. The methodology of the NI is described, and both advantages and disadvantages of the NI method are analyzed. The description of the apparatus, with the help of which the experiments on NI were carried out, is given. The basic provisions of a new model for describing the deformation properties of a nanoscale rigid two-layer structure on a porous elastic base are described. An original method of visualization of residual (after mechanical interaction) deformation in transparent and translucent materials is described. Experimentally determined values of elastic moduli and hardness of SiC nanoscale layers on Si formed by the method of coordinated substitution on three main crystal planes of Si, namely, (100), (110), and (111), and elastic moduli and characteristics (elastic modulus, hardness, strength) of surface layers of semiconductor heterostructures AlN/SiC/Si, AlGaN/SiC/Si, AlGaN/AlN/SiC/Si, GaN/SiC/Si, and GaN/AlN/SiC/Si grown on SiC/Si hybrid substrates are given. The unique mechanical properties of a new material β-Ga₂O₃ formed on SiC layers grown on Si surfaces of orientations (100), (110) and (111) are described.

The characteristics of solid surfaces are studied in this paper. Different from the local roughness method, the fractal index-surface roughness space method is proposed in this paper. Based on this method, the morphological characteristics of rubber solid surfaces are analyzed, and the theoretical leakage probability of the seals made of the corresponding rubber materials is given.

As one of the main forms of gear failure, tooth spalling makes the pit occur on the tooth surface and causes the gear not to mesh normally. Friction, an important factor in gear transmission, not only exacerbates the system vibration but also leads to the flash temperature on the tooth surface, and then the flash temperature reduces the gear stiffness. Hence, this paper reveals the relationship between gear spalling and nonlinear dynamics for a wind turbine gearbox considering friction and flash temperature. The friction force and flash temperature are calculated using Coulomb’s law and Blok’s flash temperature theory, respectively. The time-varying flash temperature stiffness and meshing stiffness of gears with spalling are separately obtained based on Hertz’s theory and potential energy method. The torsional dynamic model of the gearbox with high-speed driving gear spalling is established to study the influences of friction, flash temperature, and spalling on the dynamic behaviors, and the frequency spectrums of simulation and experiment of gear spalling are compared. The results indicate that the gear spalling and flash temperature make the comprehensive time-varying meshing stiffness decrease, and then affect the dynamic characteristics of the system in various friction states, especially dry friction. The friction and spalling change the chaotic motion interval in the high-frequency region, but the flash temperature affects the low-frequency region greatly and increases the quasi-periodic interval. The research provides significant guidance for monitoring the spalling fault of multi-stage gear transmission systems.

A new experimental method has been developed that provides a quantitative description of the evolution of damage indicators under cyclic loading of composite samples with stress concentrators. Damage parameters are defined as the deformation response to the application of an artificial cut of a given length, which extends from the contour of the central through hole in a flat rectangular sample under constant external load. Based on the test results of eight samples, the current values of damage indicators at various stages of fatigue loading were obtained. These data reveal the dependence of the required parameters on the number of loading cycles. On this basis, a damage accumulation function was constructed for the considered range of cycles. It has been established that this function refers to the first stage of the process under study. The results obtained are a necessary basis for planning further experiments.

The rationale for the prospects of using the physical and mathematical theory of metal creep in creep computations is carried out by a comparative analysis of the classical phenomenological and physical and mathematical metal creep theories. On the example of the description by both theories specific results of non-stationary creep experiments and analysis of the theories equations it is shown that implementing the physical kinetic equation for the actual structural parameter of the material, namely the scalar density of immobile dislocations, makes the physical and mathematical theory universal for solving non-stationary metal creep problems with multiaxial loading, when change, including abruptly, temperature, forces and loading rates.

The study is relevant for design modeling of the trajectory movement of vehicles on deformable support wheels. Purpose of the study: obtaining a theoretical relationship for calculating the effective normal stiffness of a deformable wheel with an inclined axis of rotation. Mathematical relationships between this stiffness and the angle of inclination of the wheel rotation axis have been established. It is determined that the effective normal stiffness changes by a factor of ({{K}_{{alpha z}}}) at the specified slope. A theoretical dependence was obtained for calculating the correction factor ({{K}_{{alpha z}}}). The dependence is a function of ({{K}_{{alpha z}}}) on the design parameters of the wheel and the angle of inclination of the rotation axis α. The dependence is correct at angles (alpha leqslant 10^circ ). At angles of inclination that are acceptable under wheel wear conditions (up to 5°) the effective normal stiffness is significantly reduced, for example, for the object of study to 25%. The validity of the theoretical dependence was confirmed by laboratory experiments using a specially created installation for measuring the parameters of the elastic properties of a deformable wheel at different positions of its rotation axis. Based on the processing of experimental data, the error in calculating ({{K}_{{alpha z}}}) from the obtained theoretical dependence was determined, which does not exceed 6%.

The article develops the quaternion regularization of differential equations (DE) of the relative perturbed motion of the body under study, which we previously proposed within the framework of the perturbed spatial problem of two bodies: the equations of motion of the center of mass of this body in a coordinate system rotating in an inertial coordinate system according to an arbitrarily given law, and also develops a quaternion DE regularization of the motion of the body under study relative to the coordinate system associated with the Earth. New quaternion DEs of the perturbed motion of an artificial Earth satellite relative to the coordinate system associated with the Earth are proposed. These equations have (in modern times) the form of DE of the relative motion of the perturbed four-dimensional oscillator in the Kustaanheimo–Stiefel variables or in our proposed modified four-dimensional variables, supplemented by DE for the energy of the satellite motion and time. These equations for the perturbed relative motion of the satellite take into account the zonal, tesseral and sectorial harmonics of the Earth’s gravitational field. The proposed equations, in contrast to classical equations, are regular (do not contain special points such as singularity (division by zero)) for the relative motion of a satellite in the Newtonian gravitational field of the Earth. The equations are convenient for applying methods of nonlinear mechanics and high-precision numerical calculations when studying the orbital motion of a satellite relative to the Earth and predicting its motion.

This study represents a comprehensive approach to propagation of Love waves in an initially stressed transversely isotropic fluid-saturated porous layer resting over a non-homogeneous half-space with irregularity at the interface. The irregularity has been taken in the form of a parabola and the displacement field in porous layer is obtained by using perturbation method. The dispersion equation has been derived for the considered model by using Biot’s theory of elasticity. Numerical simulated results have been plotted graphically with the help of MATLAB for different values of inhomogeneity parameter, anisotropic factor and initial stress and it has been observed that the phase velocity of the Love wave is influenced by various parameters such as the ratio of the depth of the irregularity to the width of the medium, wave number, initial stress, anisotropy factor and the shape of the irregularity. The findings of this study hold relevance in various fields, including materials science, geophysics and structural engineering.