Transient and Steady Sliding Friction of Elastomers: Impact of Vertical Lift

Abstract

The sliding friction of elastomers has been investigated numerically and theoretically for the line contact between a cylindrical rigid indenter and a "frictionless" Kelvin-Voigt foundation. The onset of sliding under an abrupt increase in the drive velocity has been simulated with different boundary conditions of the rigid indenter. When the rigid indenter is not allowed to move in any direction, just an abrupt change in the friction force appears, which is not accompanied by any transient processes. However, when the rigid indenter is able to move in the vertical direction, the transient sliding friction including three different time constants appears, resembling the typical transition from the static friction to the kinetic friction, in spite of no static friction considered in the simulation. The aforementioned drastic difference is caused by the "vertical lift" of the rigid indenter, which is induced by the damping of the Kelvin-Voigt foundation. In addition, the vertical lift strongly affects the characteristics of the steady sliding friction, which is explained well by using the critical velocity determined from the asymptotes in the master curve of friction coefficient.

Layered Structure and Wear Mechanism of Concentrated Polymer Brushes

“…Hence, an optimized layered structure can be employed to achieve superlubricity in the PMMA-CPB. One possible mechanism is that a decrease in the CPB thickness due to the mild wear increases the contact stiffness, causing a reduction of the indentation depth, which decreases the friction force due to the CPB viscoelasticity. , Further studies are necessary to elucidate the details of the relationship between superlubricity and the layered structure of PMMA-CPBs.…”

Two Origins for Bell-Shaped Velocity-Dependent Friction Coefficient: Kelvin-Voigt or Standard Linear Solid Viscoelasticity

“…( 9) with Eq. ( 1), we can determine the horizontal one f x (x) geometrically: (10) where we used that the local contact force subject to the probe is perpendicular to the probe surface slope at the local contact point [26]. Then, using f z (x) and f x (x) provides the contact load W, the friction force F, and the friction coefficient μ from Eqs.…”

“…One of the noteworthy characteristics of viscoelastic friction is its velocity dependence, exhibiting a bell shape in the semi-logarithmic plot of the friction Toshiki Watanabe and Ken Nakano * coefficient against the velocity, as obtained by famous Grosch's experiments [5]. Although the above theories [17][18][19][20][22][23][24][25][26][27] can explain the bell-shaped velocity-dependent friction coefficient, two origins seem hidden.…”

“…The foundation model was also applied to the sliding contact of fractal surfaces, finding a correlation between the Hurst exponent and friction coefficient [24,25]. Besides, the complete set of dimensionless numbers describing the friction coefficient has been theoretically found for sliding contacts between a single asperity with various shapes and the KV foundation [26,27]. One of the noteworthy characteristics of viscoelastic friction is its velocity dependence, exhibiting a bell shape in the semi-logarithmic plot of the friction Toshiki Watanabe and Ken Nakano * coefficient against the velocity, as obtained by famous Grosch's experiments [5].…”

Visualization of strain distribution in rubber bulk during friction

“…In an experimental investigation 14 , a master curve of µ based on the Williams-Landel-Ferry theory 15 showed that the viscoelastic properties of rubber could determine µ. The relationship between friction behavior and viscoelastic properties has been theoretically investigated based on a combined series of Kelvin elements 16,17 . Furthermore, the strain distribution during rubber friction has been investigated using the nite element method (FEM) 18-23 .…”