International Colloquium Tribology
ict
expert verlag Tübingen
125
2022
231
Wear Modeling of non-conformal Rolling Contacts subjected to Boundary and Mixed Lubrication
125
2022
Andreas Winkler
Marcel Bartz
Sandro Wartzack
ict2310417
23rd International Colloquium Tribology - January 2022 417 Wear Modeling of non-conformal Rolling Contacts subjected to Boundary and Mixed Lubrication Andreas Winkler Corresponding author: winkler@mfk.fau.de Engineering Design, Friedrich-Alexander-University Erlangen-Nürnberg (FAU), Erlangen, Germany Marcel Bartz Engineering Design, Friedrich-Alexander-University Erlangen-Nürnberg (FAU), Erlangen, Germany Sandro Wartzack Engineering Design, Friedrich-Alexander-University Erlangen-Nürnberg (FAU), Erlangen, Germany 1. Introduction The striving for frictionand wear-optimized machine elements and the associated increasing use of low-viscosity lubricants leads to a shift of operating conditions from full film lubrication to the mixed lubrication or even the boundary lubrication regime. Therefore, detailed wear simulations offer great potential for the design of machine elements: On the one hand, operating conditions with an undesirably high wear rate can be systematically avoided. On the other hand, it enables the optimization of running-in processes, which have a decisive influence on the service life of machine elements subjected to mixed lubrication or boundary lubrication. 2. Numerical Wear Modeling Within this contribution, a general method for numerical wear modeling of machine elements operated under mixed and boundary lubrication is briefly described. The entire wear-modeling scheme is implemented using a commercial FEM software. 2.1 Mixed Lubrication Model Wear simulation of the mixed lubrication regime, as depicted in Figure 1, is implemented by the application of an FEM-based EHL-Model according to H abcHi [1] to solve for the R eynolds equation: A statistical contact model of rough surfaces (e.g. G Reen wood / w illiamson -model [2]) is used to calculate the asperity contact pressure. Moreover, the surface topography model of s uGimuRa and K imuRa [3] is used to consider the time-dependent change of the surface height distribution function, which is in turn required as an input for the applied statistical asperity contact model. EHL simulation and the asperity contact model are coupled in order to fulfil the equilibrium of the load balance equation: The Profile variation is calculated by means of a RcHaRd ’s wear model [4]. Figure 1: Wear Modeling (Mixed Lubrication) 418 23rd International Colloquium Tribology - January 2022 Wear Modeling of non-conformal Rolling Contacts subjected to Boundary and Mixed Lubrication 2.2 Boundary Lubrication Model In contrast to the first mentioned approach, wear simulation of the boundary lubrication regime relies on a FEMbased contact pressure calculation, see Figure 2. This modification was implemented since EHL simulations tends to become numerically unstable in the boundary lubrication regime. Figure 2: Wear Modeling (Boundary Lubrication) In analogy to the FEM-based EHL model according to H abcHi [1], a substitute body is defined which possesses equivalent mechanical properties of the base and counter body. This substitute body is contacted with a rigid surface, which in turn possesses the equivalent geometry of the base body and the counter body, see Figure 3. Figure 3: Contact Model (Boundary Lubrication) The remaining simulation procedure is based on the mixed lubrication model as described in section 2.1. 3. Experimental Determination of the wear coefficient The aim of this wear modeling approach is to utilize a universal wear coefficient that is valid for both the boundary lubrication and the mixed lubrication wear simulations. Therefore, the wear coefficient needs to be determined in the boundary lubrication regime. But since in the mixed lubrication regime only a part of the total load is carried by the asperities, the asperity contact pressure - not the total contact pressure - is used to calculate the wear volume by means of a RcHaRd ’s wear law: A two-disc tribometer was chosen as the experimental setup for the determination the boundary lubricated wear coefficient, see Figure 4. Figure 4: Two-Disc Tribometer The material of the discs as well as their surface roughness and the lubricant ought to match the conditions of the application to be investigated. However, the geometry of the discs, the kinematics and the lubricant film thickness should be selected so as to ensure that the two-disc contact operates within the boundary lubrication regime. On the one hand, the wear volume can be determined gravimetrically and converted via the density of the disc material: On the other hand, the wear volume can also be determined by profile measurement of the worn disc. In this case, the worn cross-sectional area A wear must be determined: Finally, the wear coefficient can be calculated: 4. Conclusion and Outlook The presented wear modeling approach offers the possibility to calculate the surface profile evolution as well as the time-dependent change of the surface height distribution in any lubrication regime. Commercial FEM software is used to calculate contact pressures. Moreover, an experimental setup for the determination of the wear coefficient for a RcHaRd ’s wear law was presented. Since lubricant additives and the chemical processes at the interfaces can strongly influence the wear behavior, future research should focus to a greater extent on the influence of interface chemistry on the wear of tribological systems. 23rd International Colloquium Tribology - January 2022 419 Wear Modeling of non-conformal Rolling Contacts subjected to Boundary and Mixed Lubrication References [1] H abcHi , W., “Finite Element Modeling of Elastohydrodynamic Lubrication Problems”, John Wiley & Sons Incorporated, 2018. [2] Greenwood, J.A. et al., “Contact of nominally flat surfaces”, Proc. R. Soc. A: Math. Phys. Eng. Sci., 295, 1442, 1966, 300-319. [3] Sugimura, J. et al., “Analysis of the topographical changes due to wear”, J. Jpn. Soc. Lubr. Eng., 31, 11, 1986, 813-820. [4] Archard, J.F., “Contact and Rubbing of Flat Surfaces”, J. Appl. Phys., 24, 8, 1953, 981-988.
