Wear of Functionally Graded Coatings under Frictional Heating Conditions

Multilayered and functionally graded coatings are extensively used for protection against wear of the working surfaces of mechanisms and machines subjected to sliding contact. The paper considers the problem of wear of a strip made of a functionally graded material, taking into account the heating of the sliding contact from friction. Wear is modeled by a moving strip along the surface of a hard abrasive in the form of a half-plane. With the help of the integral Laplace transform with respect to time, the solutions are constructed as convolutions from the law of the introduction of an abrasive into the strip and the original in the form of a contour integral of the inverse Laplace transform. The study of the integrands of contour quadratures in the complex plane allowed determination of the regions of stable solutions to the problem. Unstable solutions of the problem lead to the concept of thermoelastic instability of the contact with friction and formed regions of unstable solutions. The solutions obtained made it possible to determine a formula for the coefficient of functionally graded inhomogeneity of the coating material and to study its effect on the occurrence of thermoelastic instability of the contact taking friction into account, as well as on its main characteristics: temperature, displacement, stress and wear of the functionally graded material of the coating. The effects of the abrasive speed, contact stresses and temperature on wear of the coating with the functionally graded inhomogeneity of the material by the depth were investigated.

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]

Analysis of The Influence of The Critical Speed of Thermoelastic Instability of Transfer Case on The Torque Transmission

Based on the thermoelastic instability theory, the variation trend of film thickness on the surface of transfer case friction pair is studied, and the basic process in which the thickness of lubricating oil film changes due to thermoelastic instability was obtained. According to this process, the critical speed of transfer case friction pair is used to reflect transfer torque stability. Based on above, firstly, the dynamic simulation model of the transfer case is established from which the dynamic characteristic equation of the transfer case under the combined action of asperity torque and viscous torque is obtained. Secondly, according to the result that the thickness of the transfer case lubricating oil film is affected by the joint action of lubricating oil pressure, contact pressure and thermal expansion, the condition of thermoelastic instability of the transfer case torque transmission is discussed. The result shows that the critical speed of the thermoelastic instability increases correspondingly with the increase of the thickness of the oil film. The critical curve divides the engagement process into the stable region at the upper part of the curve and the unstable region at the lower part of the curve, so as to calculate the thermoelastic instability region of the torque transfer of the transfer case. Finally, in order to further analyze the influence of thermoelastic instability on the characteristics of the transfer case, three factors, namely the surface roughness of the friction plate, the lubricating oil viscosity and the thermal conductivity of the dual steel disc, are mainly selected for analysis, and the thermoelastic instability is taken into account. The conclusion is expected to be used in the engineering practice of torque distribution control of the transfer case.

WEAR OF COATING WITH A SHEAR MODULE ARBITRALLY CHANGING BY DEPTH

The protection of the working surfaces of mechanisms in sliding contact conditions is often carried out by applying protective multilayer and functionally graded coatings, which prevent wear of the working surfaces and reduce the temperature heating of the contact. The problem of grinding the surface of oxidized and other materials with a functionally graded change in properties along the depth of the product leads to the need to control the wear rate and contact heating from friction. The effectiveness of studying the processes of wear, grinding, polishing and early diagnostics of thermoelastic instability of sliding contact is facilitated by mathematical modeling of the process of wear of products made of functionally graded materials. The thermoelastic contact problem of the wear of a functionally graded coating with an arbitrarily varying shear modulus with a hard abrasive, taking into account the heating of the contact from friction, is considered. The solutions of the problem are constructed in the form of Laplace convolutions. Analysis of the obtained solutions in the complex plane makes it possible to determine the regions of thermoelastic stability and instability of the solutions in the space of dimensionless parameters of the problem. Unstable solutions give rise to the concept of thermoelastic instability of a sliding contact. The constructed analytical solutions made it possible to study the effect of the functionally graded inhomogeneity coefficient of the coating material on the thermoelastic instability regions of the sliding contact, temperature, displacements, stresses and wear of the functionally graded coating material.