Ewa Och

Some Methods for Calculating Temperature During the Friction of Thermosensitive Materials

The thermal problem of friction for two semi-infinite bodies, with the dependence of their thermal properties on the temperature taken into account, is considered. It is assumed that a specific power of friction is constant and that a thermal contact between semi-spaces is imperfect. As a consequence of the latter assumption, the linearization of a corresponding boundary-value heat conduction problem using the Kirchhoff transformation is incomplete. Depending on the type of nonlinearity of friction body material—simple or arbitrary—the various methods of linearizing the final task are suggested. The effectiveness of these methods is illustrated by the numerical analysis of the friction materials for couples with a linear or nonlinear temperature dependence on coefficient of thermal conductivity and specific heat.

Effect of thermal sensitivity of materials of tribojoint on friction temperature

An analytical solution of a friction-heat problem for two semi-infinite solids taking into account the temperature dependence of their thermal characteristics has been obtained. It is assumed that the specific power of friction is constant and the thermal contact of the solids is imperfect. Because of the latter assumption, the linearization of the corresponding boundary heat conduction problem carried out using the Kirchhoff transform has turned out to be incomplete. Two methods for the final linearization of this problem have been proposed, i.e., the expansion of the nonlinear function in a power series, followed by the retention of only two first terms in it, and the use of linearizing multipliers. A numerical analysis for the materials with linear dependences of the thermal conductivity and the specific heat on the temperature is carried out.

Effect of the thermal sensitivity in modeling of the frictional heating during braking

The influence of the thermal sensitivity of a coefficient of friction and thermophysical properties of the pad and disk materials on the temperature distribution during single braking has been studied. For this purpose, the corresponding one-dimensional thermal problem of friction at braking has been formulated. The solution to such nonlinear problem has been made in two stages. First, the partial linearization was carried out using Kirchhoff’s substitution, and then, the initial problem for a system of nonlinear ordinary differential equations was obtained by method of lines. Numerical solution to problem was received by Adams’ method realized in the DIFSUB package. For a friction pair, disk (steel)–pad (retinax), an analysis of the evolution of sliding speed and temperature was carried out. The results obtained within the model that took into account the mutual influence between the speed and temperature were compared with those obtained without taking into account such effects.

Frictional heating during sliding of two semi-spaces with arbitrary thermal nonlinearity

Abstract Analytical and numerical solution for transient thermal problems of friction were presented for semi limited bodies made from thermosensitive materials in which coefficient of thermal conductivity and specific heat arbitrarily depend on the temperature (materials with arbitrary non-linearity). With the constant power of friction assumption and imperfect thermal contact linearization of nonlinear problems formulated initial-boundary thermal conductivity, using Kirchhoff transformation is partial. In order to complete linearization, method of successive approximations was used. On the basis of obtained solutions a numerical analysis of two friction systems in which one element is constant (cermet FMC-845) and another is variable (grey iron ChNMKh or aluminum-based composite alloy AL MMC) was conducted

CORROSION RESISTANCE OF MECHANICALLY ALLOYED 14%Cr ODS FERRITIC STEEL

Abstract The paper presents results of the corrosion resistance of mechanically alloyed oxide dispersion strengthened 14% Cr ferritic stainless. The oxide dispersion strengthened steel was prepared by means of the powder metallurgy route that consists of mechanical alloying of a pre-alloyed argon atomized steel powder (Fe-14Cr-2W-0.3Ti) with 0.3 Y2O3 (wt%), followed by HIPping at 1150°C and annealing at 850°C for 1 h. The density of ODS ferritic steel after consolidation was about 99.0% of theoretical alloy density. The potentiodynamic corrosion tests were performed for 1h and 24 h of material exposure in a physiological saline solution. For comparison the 316 LV austenitic stainless steel was also examined. The obtained results revealed that both materials were in a passive stage, however the lower current corrosion density was measured for 316 LV steel. On the contrary, the austenitic stainless steel exhibited unstable chemical processes at the passive region. On the surface of both materials localized pitting corrosion was observed with different morphology of the cavities. A broken oxide scale with poor adhesion to the ferritic steel matrix with large number of density of localized corrosion attack was observed on the surface of the ODS steel.

Modeling of the temperature regime and stress state in the thermal sensitive pad-disk brake system

An analytical–numerical nonlinear model to investigate temperature fields and thermal stresses in a pad and a disk for a single braking with a constant deceleration has been proposed. For this purpose, the boundary-value heat conduction problem for a tribosystem strip–semi-space has been formulated, which takes into account the temperature dependence of the thermophysical properties of materials. The solution to this problem has been obtained by a partial linearization through the Kirchhoff substitution, and next with a subsequent use of the method of linearizing parameters. Knowing the distribution of temperature fields in the elements of a friction pair, the thermal stresses have been established within the theory of thermal bending of plates. In this case, the temperature dependence of the Young’s modulus, Poisson’s ratio, and linear thermal expansion of the pad and disk materials have been additionally taken into account. The numerical analysis has been performed for a friction pair consisting of a titanium alloy pad and a steel disk.

SOLVING NONLINEAR THERMAL PROBLEMS OF FRICTION BY USING METHOD OF LINES

Abstract One-dimensional heat conduction problem of friction for two bodies (half spaces) made of thermosensitive materials was considered. Solution to the nonlinear boundary-value heat conduction problem was obtained in three stages. At the first stage a partial linearization of the problem was performed by using Kirchhoff transform. Next, the obtained boundary-values problem by using the method of lines was brought to a system of nonlinear ordinary differential equations, relatively to Kirchhoff’s function values in the nodes of the grid on the spatial variable, where time is an independent variable. At the third stage, by using the Adamss method from DIFSUB package, a numerical solution was found to the above-mentioned differential equations. A comparative analysis was conducted (Och, 2014) using the results obtained with the proposed method and the method of successive approximations.

THE INFLUENCE OF SALIVA AND ITS SUBSTITUTES ON CORROSION OF SOME IMPLANT ALLOYS

Abstract The purpose of this paper is evaluation of the influence of human saliva and its substitutes on the corrosion resistance of some implant alloys used in stomatology, which included: austenitic steel (316L), titanium alloy (Ti6Al4V), and cobalt alloy (CoCrMo). Corrosion studies were conducted by means of the potentiodynamic method with the application of the VoltaLab 21 kit with VoltaMaster 4 software. The reference electrode was a saturated calomel electrode (SCE), whereas the counter electrode was a platinum electrode. The results of conducted studies indicate an increased current density in the passive range on potentiodynamic curves of studied alloys in the environment of human saliva, and also in a commercial saliva solution - Mucinox. On the basis of conducted corrosion studies, it can be stated that in terms of corrosion resistance the developed saliva substitutes may constitute competitive solutions to commercial saliva substitutes. The prepared substitutes should be studied further from the perspective of practical application for patients. The original value of the paper is a proposition of new saliva substitutes.

Frictional heating of sliding semi-spaces with simple thermal nonlinearities

Abstract In the article the nonstationary thermal problem of friction for two semi-spaces with taking into account their imperfect thermal contact and thermosensitivity of materials (simple nonlinearity), has been considered. The linearization of this problem has been carried out using Kirchhoff transformation, and next using the Laplace integral transform. The analytical solution to the problem in the case of constant speed sliding, has been obtained. On the basis of the obtained solutions and using Duhamels formula, the analytical solution to the problem for sliding with constant deceleration, has been obtained, too. The results of numerical analysis are presented for two friction pairs