Finite element simulation of mixed lubrication of highly deformable elastomeric seals

The elastomeric dynamic seals with reciprocating motion are widely used in automotive and hydraulic industries. The development of elastomeric reciprocating seals is achieved mostly by trial and error methods or the engineer's prior experience. It is a challenge to design a sealing geometry with enhanced functionality, robustness under the consideration of cost efficiency at manufacturing processes. The performance of the seal is mainly determined by the tribological process in contact. This process consists of several challenging physical phenomena such as elastohydrodynamic lubrication, nonlinear material behaviour and wear. The systematic design of the seals requires better understanding of these phenomena and the investigation of the relevant parameters. The friction condition, where solid as well as the hydrodynamic friction components are present at the same time, is called mixed lubrication. The numerical modelling of mixed lubrication is a complicated task since it is primarily determined by the interaction of lubrication, deformation and contact of the asperities. The simulation model has to integrate these major effects of all three mechanisms. The coupling of nonlinear finite element computation and the solution of Reynolds equation is carried out by implementing a hydrodynamic interface element in ABAQUS Standard within the user element subroutine (UEL). The exponential contact model controls simultaneously the fluid film thickness at every node of the hydrodynamic interface element to identify the formation of the solid body contact. The contact model is implemented through the user subroutine UINTER as interface definition. The solid and hydrodynamic components of the frictional forces allow for the realistic simulation of the tangential behaviour of the reciprocating seal. Consequently, Stribeck type curves can be generated for several working conditions. An experimental work was necessary to identify the contact model parameters. With those parameters, the capability of the simulation model to reproduce the measured friction characteristic could be demonstrated. Two examples which show the potential of the simulation model conclude the thesis. In the last chapter, important results obtained with the new simulation model are presented.