Subsonic to Intersonic Transition in Sliding Friction for Soft Solids

Area of Science:

• Tribology
• Soft Matter Physics
• Materials Science

Background:

• Understanding friction in compliant materials is crucial for various applications.
• Previous studies often focused on lower sliding velocities, not exploring wave-speed regimes.
• The behavior of lubricating films under high-speed sliding against soft gels is not well understood.

Purpose of the Study:

• To investigate the friction dynamics of a compliant gel against a rigid cylinder at high sliding velocities.
• To determine the effect of sliding velocity relative to wave velocities on contact mechanics and friction.
• To develop and validate theoretical models for friction and deformation in this regime.

Main Methods:

• Performed friction experiments using a compliant gel and a rigid cylinder.
• Varied sliding velocities to be comparable to the gel's Rayleigh wave and secondary wave velocities.
• Derived theoretical solutions for contact pressure and deformation profiles.

Main Results:

• Observed a transition from Hertzian-like to flat punch-like contact when sliding velocity exceeded wave velocities.
• Documented the breakdown of the lubricating oil film under these conditions.
• Recorded an abrupt increase in the friction coefficient correlating with the contact state transition.

Conclusions:

• Sliding velocity exceeding wave velocities fundamentally alters the contact mechanics of gels.
• The derived theoretical solutions accurately predict experimental observations of pressure and deformation.
• Findings provide critical insights into high-speed friction and lubrication of soft materials.