# Elastohydrodynamics for soft solids with surface roughness: transient effects

## TL;DR

This paper models the transient elastohydrodynamic behavior of soft, rough solids in accelerated sliding, analyzing surface deformations, interface separation, and forces, with implications for biological and technological systems.

## Contribution

It introduces a theoretical framework for transient elastohydrodynamics of rough soft solids under acceleration, including surface deformation and force calculations, validated against experimental data.

## Key findings

- Squeeze-in and squeeze-out processes significantly affect the Stribeck curve.
- Transient effects alter friction and normal force during accelerated sliding.
- Theoretical results align well with experimental observations.

## Abstract

A huge number of technological and biological systems involves the lubricated contact between rough surfaces of soft solids in relative accelerated motion. Examples include dynamical rubber seals and the human joints. In this study we consider an elastic cylinder with random surface roughness in accelerated sliding motion on a rigid, perfectly flat (no roughness) substrate in a fluid. We calculate the surface deformations, interface separation and the contributions to the friction force and the normal force from the area of real contact and from the fluid. The driving velocity profile as a function of time is assumed to be either a sine-function, or a linear multi-ramp function. We show how the squeeze-in and squeeze-out processes, occurring in accelerated sliding, quantitatively affect the Stribeck curve with respect to the steady sliding. Finally, the theory results are compared to experimental data.