Improved design process of dry-running radial plastic plain bearings by coupling laboratory testing and component simulation

Up to now, the design process of dry-running radial plain bearings made of plastic for demanding applications has not been possible without cost-intensive component tests due to the fact that the calculation methods currently available are very approximate in nature and cannot be easily applied to other materials due to the necessary transfer functions in the form of diagrams. Particularly with regard to the consideration of the sliding surface temperatures occurring in the respective installation situation, there are notable weaknesses since the natural mutual dependence of the coefficient of friction, as a function of the temperature, and the temperature, in turn, as a function of the coefficient of friction and the installation condition cannot be solved easily. 

Although geometrically customizable methods exist, including finite element modeling, they require a large amount of parametrically resolved tribological material data (especially the coefficient of friction and the specific wear rate). However, the fact that these have to be determined in advance for each material by material investigations - together with the unfavorable ratio of simulated time to computation time - severely limits the practical usability of these methods for the design of components.

Therefore, a novel method for the design process of dry-running radial plain bearings is currently being developed at Leibniz-Institut für Verbundwerkstoffe (IVW). By building a computer-aided calculation model of a plain bearing and coupling it with a block-on-ring wear test bench, a control loop ("hardware-in-the-loop", see Figure 1) is created that simulates the real behavior of a plain bearing. The plastic block used corresponds to a segment of a plain bearing at its most heavily loaded point. By continuously passing on the test rig measured variables of sliding friction coefficients µ and block height h_block during the running test, the computer calculates in-situ the corresponding current operating state of a virtual plain bearing. By means of a thermal calculation model, the temperature of the virtual shaft is calculated from the sliding friction coefficient µ and the geometric and material-specific boundary conditions entered. Based on the transmitted wear-related change in block height h_block, the wear-related change in geometry of the virtual bearing is first calculated which in turn is used to calculate the respective current surface pressure distribution in the virtual journal bearing. These two calculation results - more precisely: the equivalent normal force resulting from the surface pressure and the mating body temperature - are transmitted to the test rig and adjusted accordingly. This procedure is carried out iteratively and continuously. Thus, both the surface pressure prevailing in the further course of the aBoR test and the temperature of the ring test specimen no longer result, as before, only from the frictional power of the block-ring test specimen pair and the heat dissipation dependent on the respective test rig design but are set according to the results of the simulation of a plain bearing running during the test.

Contakt:

Dipl.-Ing. Marc Fickert
Wissenschaftlicher Mitarbeiter
Kompetenzfeld Tribologie
Leibniz-Institut für Verbundwerkstoffe GmbH
Erwin-Schrödinger-Straße 58
Telefon: +49 631 2017-285
Email: marc.fickert@ivw.uni-kl.de