Friction dampers—Everything old is new again

Abstract

The title is suggested by a delightful song and dance scene in the film “All That Jazz” (1979). Due to the author's lack of grace, rather than repeating that performance, the presentation will explore a concept suggested by the friction draft gear patented by George Westinghouse in 1888. It and variants are in wide use throughout the North American railroad system. The idea to be examined exploits the fact that the normal forces on the faces of a wedge are greatly magnified, thereby enhancing the friction force associated with the Coulomb friction model. Because of this behavior a simple oscillator whose moving mass is a spring-loaded wedge can absorb much more vibrational energy than other passive techniques. Dynamic analysis of a one-degree-of-freedom model leads to an algebraic expression for the energy dissipated per unit cycle. That formula indicates that critical damping ratios much greater than one are readily obtainable if the springs are precompressed sufficiently. The simplicity of the underlying physical system implies that it is scalable over a large range, from MEMS to seismic structures. A particularly interesting idea is to fabricate a metamaterial consisting of an array of wedge dampers.The title is suggested by a delightful song and dance scene in the film “All That Jazz” (1979). Due to the author's lack of grace, rather than repeating that performance, the presentation will explore a concept suggested by the friction draft gear patented by George Westinghouse in 1888. It and variants are in wide use throughout the North American railroad system. The idea to be examined exploits the fact that the normal forces on the faces of a wedge are greatly magnified, thereby enhancing the friction force associated with the Coulomb friction model. Because of this behavior a simple oscillator whose moving mass is a spring-loaded wedge can absorb much more vibrational energy than other passive techniques. Dynamic analysis of a one-degree-of-freedom model leads to an algebraic expression for the energy dissipated per unit cycle. That formula indicates that critical damping ratios much greater than one are readily obtainable if the springs are precompressed sufficiently. The simplicity of the underlyin...