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Static friction coefficient depends on the external pressure and block shape due to precursor slip
Wataru Iwashita1, Hiroshi Matsukawa2, Michio Otsuki3
1Department of Mechanical Science and Bioengineering, Osaka University, Toyonaka, 560-8531, Japan. w_iwashita@fm.me.es.osaka-u.ac.jp.
Scientific Reports
|February 13, 2023
Summary
This study challenges Amontons' law by showing that the macroscopic static friction coefficient decreases with object size and pressure. Precursor slip and critical slip area govern this phenomenon in viscoelastic materials.
Area of Science:
- Tribology
- Materials Science
- Solid Mechanics
Background:
- Amontons' law posits friction is independent of contact area and external pressure.
- This study investigates deviations from Amontons' law in viscoelastic materials.
Purpose of the Study:
- To numerically investigate the sliding motion of a 3D viscoelastic block on a rigid substrate.
- To identify the factors causing macroscopic static friction to deviate from Amontons' law.
Main Methods:
- Finite Element Method (FEM) simulations of a 3D viscoelastic block.
- Theoretical analysis of simplified models.
Main Results:
- Macroscopic static friction coefficient decreases with increased external pressure, length, and width.
- Precursor slip observed at the 2D interface before bulk sliding.
- Decrease in friction coefficient is scaled by the critical area of precursor slip.
Conclusions:
- Bulk sliding arises from precursor slip instability due to velocity-weakening friction.
- The critical slip area dictates the macroscopic static friction coefficient, explaining simulation results.
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