Editing Friction (section)

===Dry friction and instabilities===
Dry friction can induce several types of instabilities in mechanical systems which display a stable behaviour in the absence of friction.<ref>{{cite book |last=Bigoni |first=D. |title=Nonlinear Solid Mechanics: Bifurcation Theory and Material Instability |publisher=Cambridge University Press, 2012 |isbn=978-1-107-02541-7|date=2012-07-30 }}</ref>
These instabilities may be caused by the decrease of the friction force with an increasing velocity of sliding, by material expansion due to heat generation during friction (the thermo-elastic instabilities), or by pure dynamic effects of sliding of two elastic materials (the Adams–Martins instabilities). The latter were originally discovered in 1995 by [[George G. Adams (engineer)|George G. Adams]] and [[João Arménio Correia Martins]] for smooth surfaces<ref>{{cite journal |last=Adams |first=G. G. |title=Self-excited oscillations of two elastic half-spaces sliding with a constant coefficient of friction |doi=10.1115/1.2896013 |journal=Journal of Applied Mechanics |year=1995 |volume=62 |issue=4 |pages=867–872 |bibcode=1995JAM....62..867A }}</ref><ref>{{cite journal |last=Martins |first=J.A., Faria, L.O. & Guimarães, J. |title=Dynamic surface solutions in linear elasticity and viscoelasticity with frictional boundary conditions |doi=10.1115/1.2874477 |journal=Journal of Vibration and Acoustics |year=1995 |volume=117 |issue=4 |pages=445–451}}</ref> and were later found in periodic rough surfaces.<ref>{{cite journal |last1=M |first1=Nosonovsky |last2=G. |first2=Adams G. |title=Vibration and stability of frictional sliding of two elastic bodies with a wavy contact interface |doi=10.1115/1.1653684 |journal=Journal of Applied Mechanics |year=2004 |volume=71 |issue=2 |pages=154–161 |bibcode=2004JAM....71..154N }}</ref> In particular, friction-related dynamical instabilities are thought to be responsible for [[Brake#Noise|brake squeal]] and the 'song' of a [[glass harp]],<ref>{{cite journal |last2=J. |first2=Hultén |last1=J. |first1=Flint |title=Lining-deformation-induced modal coupling as squeal generator in a distributed parameter disk brake model |doi=10.1006/jsvi.2001.4052 |bibcode=2002JSV...254....1F |journal= Journal of Sound and Vibration|year=2002 |volume=254 |issue=1 |pages=1–21}}</ref><ref>{{cite journal |last1=M. |first1=Kröger |last2=M. |first2=Neubauer |last3=K. |first3=Popp |s2cid=16395796 |title=Experimental investigation on the avoidance of self-excited vibrations |journal=Phil. Trans. R. Soc. A |doi=10.1098/rsta.2007.2127 |year=2008 |pages=785–810 |volume=366 |issue=1866 |pmid=17947204 |bibcode=2008RSPTA.366..785K }}</ref> phenomena which involve stick and slip, modelled as a drop of friction coefficient with velocity.<ref>{{cite journal |last2=L. |first2=Ruina, A. |last1=R. |first1=Rice, J. |title=Stability of Steady Frictional Slipping |journal=Journal of Applied Mechanics |volume=50 |year=1983 |pages=343–349 |url=http://ruina.tam.cornell.edu/research/topics/friction_and_fracture/stability_steady.pdf |archive-url=https://web.archive.org/web/20100622193459/http://ruina.tam.cornell.edu/research/topics/friction_and_fracture/stability_steady.pdf |archive-date=2010-06-22 |url-status=live |doi=10.1115/1.3167042 |issue=2 |bibcode=1983JAM....50..343R |citeseerx=10.1.1.161.5207 }}</ref>

A practically important case is the [[self-oscillation]] of the strings of [[bowed instruments]] such as the [[violin]], [[cello]], [[hurdy-gurdy]], [[erhu]], etc.

A connection between dry friction and [[Aeroelastic flutter#Flutter|flutter]] instability in a simple mechanical system has been discovered,<ref>{{cite journal
 |url          = http://www.ing.unitn.it/~bigoni
 |author1      = Bigoni, D.
 |author2      = Noselli, G.
 |title        = Experimental evidence of flutter and divergence instabilities induced by dry friction
 |journal      = Journal of the Mechanics and Physics of Solids
 |year         = 2011
 |volume       = 59
 |pages        = 2208–2226
 |doi          = 10.1016/j.jmps.2011.05.007
 |issue        = 10
 |bibcode      = 2011JMPSo..59.2208B
 |citeseerx    = 10.1.1.700.5291
 |access-date  = 2011-11-30
 |archive-date = 2020-08-18
 |archive-url  = https://web.archive.org/web/20200818112658/http://www.ing.unitn.it/~bigoni/

}}</ref> watch the [http://www.ing.unitn.it/~bigoni/flutter.html movie] {{Webarchive|url=https://web.archive.org/web/20150110065917/http://www.ing.unitn.it/~bigoni/flutter.html |date=2015-01-10 }} for more details.

Frictional instabilities can lead to the formation of new self-organized patterns (or "secondary structures") at the sliding interface, such as in-situ formed tribofilms which are utilized for the reduction of friction and wear in so-called self-lubricating materials.<ref>{{cite book
| title = Friction-Induced Vibrations and Self-Organization: Mechanics and Non-Equilibrium Thermodynamics of Sliding Contact
| first = Michael
| last = Nosonovsky
| year = 2013
| publisher = CRC Press
| isbn = 978-1-4665-0401-1
| url = http://www.crcpress.com/product/isbn/9781466504011
| page = 333}}</ref>