Prof. Jim Woodhouse (University of Cambridge, UK)
Feb 28, 2017
from 02:00 PM to 03:00 PM
|Contact Name||Felix Hofmann|
|Add event to calendar||
Vibration excited by friction can be unwanted, as in vehicle brake squeal, or it can be intentional, as in a bowed violin string. In either case there are good reasons to want to be able to predict and control the vibration. Modelling of the linear component of vibrating systems is well understood, but a sufficiently accurate model for the dynamic friction force at an interface is another matter. Many models have been proposed, but none has a very good track record for reliable prediction. This talk will describe recent work in which some useful progress has been made on this old and thorny problem. Both the applications mentioned above will be discussed: they raise significantly different questions, and turn out to require different styles of modelling. To predict the threshold of instability for a phenomenon like brake squeal, it will be argued that a kind of frequency response function of sliding friction is needed. Recent work to measure and model this function will be described. For the violin string, the focus switches to the tougher challenge of predicting transient details of the vibration, not just the threshold. Various candidate models will be compared with measurements, and it will be argued that for friction mediated by violin rosin the most important controlling variable is the contact temperature. However, a fully accurate model still eludes us at present.