Thermoelastic instability during sliding of inhomogeneous materials with different thermophysical properties

The conditions for the appearance of thermoelastic instability are determined by modeling of the frictional heating during sliding of the surface of an inhomogeneous material having a periodic structure, consisting of elements with different thermophysical properties. Cases of the absence of wear and steady-state wear conditions with a linear dependence of the wear rate on the applied pressure and sliding speed are considered. Keywords: inhomogeneous material, matrix, fiber, thermoelastic instability, wear, periodic structure. [email protected]

On Durability of Structurally Inhomogeneous Materials

Numerical methods used to calculate strength are based on energy approaches and minimization of functionals of one type or another. Yet the model of a material is limited to stable processes of deformation. As a result, a considerable number of deformation properties related to realization of the softening stage in materials of structural elements remains unaccounted for. To describe fracture as a new phenomenon in the behavior of structures, one needs to apply newer experimental and calculational approaches. The article cites results of modelling and experimental notions on the stage of softening in materials and its role in determining their durability. It is proposed to define the durability of a structurally inhomogeneous material as its capacity of equilibrium deformation beyond its ultimate strength under specified loading conditions. That reflects nonlocality of criteria for the failure of the material, their dependence both on its own properties and the geometry of a structural element. Complete stress-strain diagrams for structural materials of various classes and examples on how the softening stage is realized in structural materials are given.

ANALYSIS OF METHODS FOR CALCULATING SPUR GEAR FOR DEEP CONTACT STRENGTH

Spur gear is an integral part of transport and technological machines structure. To increase the load ability of the spur gear, chemical heat treatment of the working cogs surfaces is used. Spur gear with chemical heat treatment must be checked for deep contact strength. The article analyzes various methods (according to GOST 21354-87, methods using the generalized criterion of the limit state for structurally inhomogeneous material by Lebedev-Pisarenko, methods from the handbook describing reducers of power machines etc.) for calculating spur and helical gearing for deep contact strength. The author presents all necessary formulas and graphs for the implementation of each methods, and compares the calculations results of these methods with the results of experimental studies of cemented cylindrical rollers for deep contact destruction.

Modeling of the Process of Deformation of Inhomogeneous Material in the Closed Die

The issues of physical modeling of the processes of deforming inhomogeneous materials are extremely relevant in the development of adequate models of technological processes for the processing of materials by pressure. The object of research is the technology of draft of inhomogeneous material in a closed die. The subject of the research is the processes of evolution of the structure of inhomogeneous material during its deformation. The paper presents a technique that allows to fix the dynamics of compaction of a inhomogeneous flat sample in the process of its draft in a closed die at different rates of deformation and contact conditions in the system «sample – matrix – punch». As a result of the experimental study of the process of draft of inhomogeneous material in a closed matrix, the data characterizing the pore formation and distribution of forces depending on the friction factor, the deformation rate and the degree of deformation are obtained. A method of estimating changes in the geometric parameters of pores in the deformation process is proposed, which allows to determine the front of the material compaction. The obtained experimental data can be used to construct a model describing the deformation of an inhomogeneous medium taking into account the compressibility of the material.