Professor of Solid and Structural Mechanics

# Flutter induced by friction

We provide the first definitive experimental evidence that flutter instability (a blowing-up vibrational motion) and divergence instability (an exponentially growing motion) can be induced by dry friction in a mechanical system that would be stable in the absence of frictional forces. We show that Coulomb friction produces a follower load of the type studied, among others, by Ziegler.*If you're having trouble playing videos on YouTube,*

*click here to watch it.*# Structures loaded with a force acting along a fixed straight line, or the "Reut's column problem"

An elastic double pendulum subject to a force acting along a fixed straight line, the so-called "Reut's column problem", is a structure exhibiting flutter and divergence instability, which was never realized in practice and thus debated whether to represent reality or mere speculation. It is shown, both theoretically and experimentally, how to obtain the Reut's loading by exploiting the contact with friction of a rigid blade against a freely-rotating cylindrical constraint, which moves axially at constant speed, an action recalling that of a bow’s hair on a violin string. With this experimental set-up, flutter and divergence instabilities, as well as the detrimental effect of viscosity on critical loads, are documented indisputably, thus bringing an end to a long debate. This result opens a new research area, with perspective applications to mechanical actuators, high-precision cutting tools, or energy harvesting devices.*If you're having trouble playing videos on YouTube,*

*click here to watch it.***Related papers:**

- D. Bigoni and G. Noselli
Experimental evidence of flutter and divergence instabilities induced by dry friction.
*Journal of the Mechanics and Physics of Solids*, 2011, 59, 2208-2226. - D. Bigoni, Nonlinear Solid Mechanics Bifurcation Theory and Material Instability. Cambridge University Press, 2012, ISBN:9781107025417.
- D. Bigoni, D. Misseroni, G. Noselli, D. Zaccaria Surprising instabilities of simple elastic structures. In
*Nonlinear Physical Systems - Spectral Analysis, Stability and Bifurcations*, Kirillov, N. and Pelinovsky, D.E. Eds., Wiley, pp. 1-14, 2014; ISBN: 978-1-84821-420-0. -
Bigoni, D., Misseroni, D. (2019).

Structures loaded with a force acting along a fixed straight line, or the "Reut's column problem".

*Journal of the Mechanics and Physics of Solids*,**134**, 103741.

doi: https://doi.org/ 10.1016/j.jmps.2019.103741

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