Simulation is more than Software

Free Trial Version
0
Wishlist
0 0
Cart

Directcontact
EN
Simulating stick-slip and friction oscillation
Schleifring GmbH turned to CADFEM to analyze electric sliding contacts using simulation in order to avoid unwanted vibrations.

Slip-stick and other friction-induced oscillations

Sector: Machinery and plant engineeringSpecialist field: Structural mechanics

SCHLEIFRING GmbH, with support from CADFEM and Ansys simulation tools, analyzed the factors relevant to excitation mechanisms in an electric sliding contact in order to avoid undesirable oscillations that can occur with friction.

Summary

Task

An electric sliding contact relies on a stable sliding contact state without oscillatory instabilities. This means that the stationary sliding state must remain stable against small disturbances for the given set of friction parameters.

Solution

After solving the initial steady state friction condition in a nonlinear static contact analysis, some of the most important phenomena of friction instability were analyzed.

Customer benefits

CADFEM succeeded in implementing an insightful simulation environment for the oscillation behavior of the electric sliding contact. The three influencing factors – mode coupling, stick-slip effect and negative damping due to velocity-dependent friction – could all be analyzed in detail using simulation.

Project Details

Task

Self-excited friction-induced oscillations occur in various technical applications. Typical examples are irritating noise problems that occur in squeaking brakes, railroad wheels or door hinges. Moreover, due to the inherent instability of the oscillations, the same mechanism can even lead to malfunctions. An electric sliding contact, for example, relies on a stable sliding contact state without oscillatory instabilities. This means that the stationary sliding state must remain stable against small disturbances for the given set of friction parameters.


Customer Benefit

CADFEM succeeded in implementing an insightful simulation environment for the oscillation behavior of the electric sliding contact. The three influencing factors – mode coupling, stick-slip effect and negative damping due to velocity-dependent friction – could all be analyzed in detail using simulation.


Solution

After solving the initial steady state friction condition in a nonlinear static contact analysis, some of the most important phenomena of friction instability were analyzed.

  • Mode coupling instability: two initially separate modes coincide and exchange energy as friction increases, damping one mode and exciting the other. This is done using a complex modal analysis that takes the unsymmetric stiffness matrix into account.
  •  Stick-slip effect: an alternation of sticking and sliding phases leads to the typical sawtooth behavior shown in the diagram. This requires a nonlinear transient analysis, with appropriate contact settings and a suitable time-step strategy.
  • Negative damping for some modes due to the decreasing velocity-dependent friction law. A nonlinear transient analysis results in increasing harmonic behavior (see diagrams).

Images: © SCHLEIFRING


Head of Professional Development
Dr.-Ing. Marold Moosrainer

Related products and training offers