What determines static friction and controls the transition to sliding?

Günter Reiter, A. Levent Demirel, John Peanasky, Lenore Cai, Steve Granick

Research output: Contribution to journalArticle

9 Scopus citations

Abstract

We studied the shear response of a confined lubricant layer on approach of the transition to sliding with a surface force apparatus modified for oscillatory shear. In a given experiment, we found that the transition to sliding occurred always around the same deformation amplitude although the shear stress needed to initiate sliding varied up to a factor of two depending on sample history. This suggests the concept of deformation-controlled switching from rest to sliding. The elastic spring-constant, in the stick state, weakened with increasing deformation amplitude. This decrease can be described by a power law when plotted versus the distance to a critical deformation amplitude. The build-up of solid-like behavior after sliding stopped was also gradual and was consistent with a logarithmic time dependence. We suggest a model relating the gradual decrease of stiffness to weakening of the boundary layer, specifically to destruction of some elastic links between molecules or between molecules and the solid surfaces. Static friction (the force that must be overcome at the onset of kinetic motion) is proportional to the number of such links formed during the time of stick.

Original languageEnglish (US)
Pages (from-to)1-12
Number of pages12
JournalTribology Letters
Volume1
Issue number1
DOIs
StatePublished - Jun 1 1995
Externally publishedYes

Keywords

  • confined liquid lubricant
  • deformation threshold
  • history-dependent shear response
  • static friction
  • surface force apparatus

ASJC Scopus subject areas

  • Mechanics of Materials
  • Mechanical Engineering
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films

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