Badania termomechanicznej niestabilności hamulców przemysłowych

This paper presents disc brake surface temperature field measurements, during emergency braking in real industrial conditions, by means of the thermovision infrared camera. The temperature field assessment enables the verification of the numerical modelling of the brake performance in the succeeding step. The experimental part of the research also covers tribological testing on the coefficient of friction between the friction brake material (brake pad) and steel (brake disc) in laboratory conditions on a tribotester which satisfied the similarity criteria with the mine winder hydraulic disc brake. The tribological characteristic of the friction couple, including the kinetic and static coefficients of friction, were determined for use in the finite elements analysis (FEA) of the brake thermo-mechanical instability (TMI) problem. In the numerical part of this work, the FE modelling technique was used to simulate the brake interface hot spotting and the axial disc distortion as a function of the geometrical and material properties of the brake elements and the brake’s operational conditions. The critical speed above which TMI would occur was calculated for the analysed mine winder brake system. A FE method was used to find the temperature distribution and the resulting thermal stresses and distortions in the brake discs. The disc division into various numbers of sections was numerically tested for the division’s effect on thermal stress reduction and axial distortions.Artykuł przedstawia wyniki badań rozkładu temperatur na powierzchni tarczy hamulcowej w czasie hamowania awaryjnego maszyny z użyciem kamery termowizyjnej. Uzyskane wyniki umożliwiły weryfikację obliczeń numerycznych tego procesu hamowania. Przedstawiono także badania tribologiczne charakterystyki ciernej pary hamulcowej, czyli materiału okładziny hamulcowej i materiału tarczy hamulcowej. Badania tribologiczne wykonano na stanowisku spełniającym najważniejsze kryteria podobieństwa do hamulca tarczowego maszyny wyciągowej. Uzyskane wartości współczynników tarcia kinetycznego i statycznego były wykorzystane następnie w modelowaniu numerycznym termomechanicznej niestabilności analizowanego hamulca i wyznaczeniu krytycznej prędkości początkowej, powyżej której system staje się niestabilny. Obliczenia numeryczne obejmowały także wyznaczenie naprężeń termicznych w tarczy, deformacji osiowej tarczy oraz wpływu podziału tarczy na segmenty na naprężenia i jej deformacje osiowe

Some aspects of IR temperature measurements of a disc during experimental investigations of disc brakes

Przedstawiono wybrane wyniki badań hamulca tarczowego na stanowisku laboratoryjnym. W trakcie doświadczeń mierzone były główne parametry procesu hamowania oraz rozkłady temperatury w klocku i na powierzchni tarczy hamulcowej za pomocą kamery termowizyjnej. Zebrane dane pomiarowe stanowią materiał do weryfikacji modeli matematycznych przy numerycznej symulacji działania tego typu hamulców. Głównym tematem tej pracy jest analiza zmian współczynnika emisyjności powierzchni tarczy w warunkach prowadzenia eksperymentów. Znajomość stwierdzonych prawidłowości jest przydatna przy planowaniu i prowadzeniu tego typu badań.Selected results of testing a disc brake on the laboratory stand, Fig. 1, are presented. There were measured the parameters of braking mechanics as well as the temperature distribution in a brake block and on the disc surface. The temperature distribution was determined with use of an infrared camera. The obtained measurement data were used for verification of the mathematical models for numerical simulations of brakes operation. The problems in determination of the disc surface emissivity coefficient and the character of its changeability during experiments at different braking parameters, Figs. 58, were the objectives of the project. The measurements of the emissivity coefficient on the entire disc surface were taken repeatedly, Figs. 2, 3. A correlation between the disc emissivity coefficient and the mechanical parameters of braking was found. Despite the fact that these correlations are qualitative rather than quantitative, they are interesting from the point of view of identification of the braking process as well as of planning such experiments. During the measurements, some interesting practical experience in the field of infrared measurements of temperature of the surface of not high emissivity coefficient was gained. In the project an isothermal protective screen was applied to normalize the radiation impact of the environment on the measurements, Figs 1, 4

A survey and comparison of several friction force models for dynamic analysis of multibody mechanical systems

This study is aimed at examining and comparing several friction force models dealing with different friction phenomena in the context of multibody system dynamics. For this purpose, a comprehensive review of present literature in this field of investigation is first presented. In this process, the main aspects related to friction are discussed, with particular emphasis on the pure dry sliding friction, stick–slip effect, viscous friction and Stribeck effect. In a simple and general way, the friction force models can be classified into two main groups, namely the static friction approaches and the dynamic friction models. The former group mainly describes the steady-state behavior of friction force, while the latter allows capturing more properties by using extra state variables. In the present study, a total of 21 different friction force models are described and their fundamental physical and computational characteristics are discussed and compared in details. The application of those friction models in multibody system dynamic modeling and simulation is then investigated. Two multibody mechanical systems are utilized as demonstrative application examples with the purpose of illustrating the influence of the various frictional approaches on the dynamic response of the systems. From the results obtained, it can be stated that both the choice of the friction force model and friction parameters involved can significantly affect the simulated/ modeled dynamic response of mechanical systems with friction.The first author expresses his gratitude to the Portuguese Foundation for Science and Technology through the PhD grant (PD/BD/114154/2016). This work has been supported by the Portuguese Foundation for Science and Technology with the reference project UID/EEA/04436/2013, by FEDER funds through the COMPETE 2020—Programa Operacional Competitividade e Internacionalização (POCI) with the reference project POCI-01-0145-FEDER-006941.info:eu-repo/semantics/publishedVersio