Loading Mode-Induced Enhancement in Friction for Microscale Graphite/Hexagonal Boron Nitride Heterojunction

Area of Science:

• Materials Science
• Tribology
• Nanotechnology

Background:

• Classical friction models assume constant friction regardless of normal load.
• Microscale friction dynamics often deviate from macroscopic observations.
• Understanding load distribution is crucial for predicting friction behavior.

Purpose of the Study:

• To investigate the effect of altered loading modes on micro graphite flake friction.
• To challenge the traditional assumption of constant friction under varying load conditions.
• To explore methods for enhancing friction at the microscale for potential macroscale applications.

Main Methods:

• Utilized atomic force microscopy (AFM) to apply and manipulate loads on single graphite flakes.
• Introduced a cap to disperse the normal load, altering force concentration.
• Employed finite element analysis (FEA) to model stress distribution and its effect on friction.

Main Results:

• Dispersing the normal load on micro graphite flakes resulted in a 4-7 fold increase in lateral friction.
• FEA confirmed that load dispersion increases compressive stress at flake edges, enhancing friction.
• Demonstrated that loading mode is a critical factor in microscale friction, not just normal load.

Conclusions:

• Friction is not constant with a given normal force; loading mode significantly influences microscale friction.
• Load dispersion offers a novel strategy to increase friction in micro-devices.
• The findings pave the way for assembling microscale superlubricity (SSL) graphite flakes for macroscale SSL applications.