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MU 1225/36-1

Context

Seals are an essential machine element in hydraulic components. They prevent leakage and sealing of volumes makes a pressure build-up possible in the first place. Seals are among the cheapest components of a system, but their failure often has an enormous influences and can even lead to a total system failure. Leakage-, friction and wear behaviour are profoundly non-linear and inadequately understood. The development and design of sealing systems is mostly based on expert knowledge, design guidelines and experiments. Previous elastohydrodynamic considerations focused on stationary, non-accelerated conditions. A reliable dynamic approach, taking into account the strong interactions between a large number of relevant influencing factors, has not been established.

Objective

Within this research project a theoretical, experimental validated model of translational hydraulic seals in consideration of transient processes should be developed. The model should be designed without limitation of size scales, from the macroscopic sealing to the microscopic surface structures, which significantly influence the contact mechanic, friction and fluid transport in the contact zone, and shall provide a physically based description. The close interdisciplinary cooperation with the Forschungszentrum Jülich allows a combination of methods of the natural and engineering sciences.

Simulation

For a physically based simulation of translational hydraulic seals contributions from both solid and fluid contact are considered (figure 1). The transient Reynolds equation is applied for the computation of the fluid film. The solid contact calculation and the consideration of microscopic effects are based on Persson’s theory of contact mechanics [1], [2]. The calculations are implemented in a dynamic finite element analysis, using the commercial tool ABAQUS. An exemplary simulated fluid pressure built-up and the corresponding seal deformation are shown in the following animation.

Fig. 1: Structure of the elastohydrodynamic simulation

Experimental validation

For the experimental investigation of a lubricated sealing contact a test rig was designed and set up at the Institute for Fluid Power Drives and Controls (IFAS) [3], [4].. A seal specimen is brought in contact with a rotating test cylinder (figure 2). Thus, dynamic and quasi stationary measurements can be carried out. An exemplary comparison of simulation and measurement is shown in figure 3.

Fig. 2: CAD picture of the test rig. A detailed view of the contact zone and the corresponding FE model are shown on the bottom


Fig. 3: Exemplary comparison of simulation and measurement

Acknowledgement

The research work is performed within a Reinhart-Koselleck project funded by the Deutsche Forschungsgemeinschaft (DFG). We would like to thank DFG for the project support under the reference German Research Foundation DFG-Grant: MU 1225/36-1.

Literature

[1] - Persson, B. N. J., "Theory of rubber friction and contact mechanics,” The Journal of Chemical Physics, vol. 115, no. 8, p. 3840, 2001.
[2] - M. Scaraggi and Persson, B. N. J., "General contact mechanics theory for randomly rough surfaces with application to rubber friction,” The Journal of chemical physics, vol. 143, no. 22, p. 224111, 2015.
[3] - J. Angerhausen, H. Murrenhoff, L. Dorogin, M. Scaraggi, B. Lorenz and Persson, B. N. J., "Influence of anisotropic surfaces on the friction behaviour of hydraulic seals,” Proceeding of the 2016 Bath/ASME Symposium on Fluid Power and Motion Control, 2016.
[4] - J. Angerhausen and H. Murrenhoff, "Influence of anisotropic surfaces on the friction behaviour in hard/soft line contacts,” 19th International Sealing Conference, 2016.

Sachbearbeiter

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