Two FEM Approaches for the Prediction and Quantification of “Stick-Slip” Phenomena on Rubber-Metal Sliding Contacts

The stick-slip phenomenon constitutes a challenge when referring to tribological design of rubber sealing components in a wide range of pneumatic and hydraulic applications. Several systems such as brake and clutch servo actuators, hydraulic gearshifts and other actuation systems are influenced by this phenomenon which is commonly associated to system control problems (system vibrations & noise) and to the reduction of the service life of rubber sealing components. Under a macroscopic point of view, the stick-slip consists on the sudden and successive change of the state of relative movement between two sliding surfaces in contact from “static” to “sliding”.

In the present paper, two FEM-based approaches are presented with the final objective of developing a numerical predictive tool for the analysis and quantification of this undesired phenomenon. First approach is based on a common existing in literature mass-spring system over a moving surface and implemented into a parametrized FE modelling. The methodology based on the parametrization of the FE simulations allows to study the influence of several system variables such as the frictional force evolution, the mass of the system, the system stiffness and damping and also sliding speed on the frequency and amplitude of the stickslip instability. All the system variables corresponding to the simplified mass-spring model are connected to the real system in the way that an analysis or proposed modification on any of them can be directly translated into effective modifications of the real system to prevent “stick-slip” events.

As an alternative approach to the direct FE simulation, a more affordable technique like the complex eigenvalue analysis of the problem is also applied to this example in order to obtain system instabilities. Even though this technique is more suitable for the analysis of mode-coupling friction instabilities, it is shown that the results in terms of eigenvalues can compared and correlated to the time domain simulation results. Finally, a comparison of both approaches is carried out with the objective of developing a low-time-consuming tool with reasonable accuracy for predicting and quantifying stick-slip phenomena on real rubber sealing components.

Key words: Tribology, polymers, “stick-slip”, friction, finite element method, user subroutine, parametrization, complex eigenvalue analysis.