Friction -induced vibrations and squeal of glass -run window sealing systems
Abstract
Friction-induced vibrations may in certain conditions cause squeal noise to occur. Squeal may be generated in partly wet glass-run window systems due to the friction between the seal surface and the window. Squeal noise causes annoyance and conveys a subjective impression of poor vehicle quality. The transient vibrations and sound featured an increase in amplitude with high fundamental frequency in the experiment of a seal sample and a moving glass panel. Multiple harmonics of the fundamental frequency and frequency jumps were observed in vibration frequency spectra. The frequency decreased as the amplitude of the vibration increased, which is characteristic of stick-slip oscillations. The vibrations occurred when there was a large decrease of the friction force during a surge in speed. An approximate expression for the frequency of the stick-slip oscillations was obtained in a single-degree of freedom model. The model indicated that the frequency decreased as the normal force and the difference between the static and kinetic friction coefficients were increased. The seal was idealized as a continuous one-dimensional rod, and the glass was represented as a sliding, concentrated contact force. The system became unstable when the magnitude of the normal force and the magnitude of the negative slope in the friction law were large. Harmonics of the fundamental frequency were observed in spectrograms of the responses. The frequency was shifted between modal frequencies because of modal amplitude variations with the position of the contact force. Stick-slip oscillations were simulated in a finite element model using an explicit time marching method. Slipping occurred locally in regions of the seal surface where the elastic force overcame the static friction force. The stick-slip phenomenon was found to propagate between the speeds of dilatational and transverse waves. The motion of the seal at the slipping phase was in the direction of friction force. The peak frequency was found to vary according to the glass position on the seal surface. It was suggested that both periods of stick motion and slip motion should be considered in order to estimate the frequency of the stick-slip oscillations.
Degree
Ph.D.
Advisors
Krousgrill, Purdue University.
Subject Area
Mechanical engineering
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