The Interplay of System Dynamics and Dry Friction: Shakedown, Ratcheting and Micro-Walking

This thesis discusses the influence of vibrations in dynamic systems with dry friction. As a generic model for a force locked connections under the influence of vibrations, the so called oscillating rolling contact is introduced. It consists of a tangentially loaded contact between two bodies, where the upper body follows an oscillating rocking motion. It shows that the oscillatory rolling influences the pressure distribution and the contact region. Together with the tangential load, this rocking motion causes incremental sliding processes and a rigid body motion. In case that the rolling amplitude is sufficiently small, the slip ceases after the first few periods. The residual force in the contact withstands the tangential load and the system reaches a new equilibrium: a so called shakedown occurs. Otherwise a continuing rigid body motion is induced where one side of the contact alternately sticks, while the other slips. This effect is referred to as ratcheting. Analytical failure criteria, i. e. the so called shakedown limits, are derived as a function of the rolling amplitude and the tangential load. These are in very good agreement with the experimental results and simulations. In order to examine the influence of system dynamics on sliding friction, the microwalking machine is introduced as a model. The results show that the frictional resistance almost vanishes if a certain parameter range is met. This effect is referred to as microwalking and leads to a theoretical reduction of the frictional resistance of up to 98 %. Following the analysis and identification of the relevant parameter ranges for all of the three effects, their occurrence in technical systems discussed. In addition guidelines are given for possible technical applications: