An experimental study on the relation between friction force and real contact area

Area of Science:

• Tribology
• Materials Science
• Physics

Background:

• Classical friction laws state friction is proportional to normal load and independent of contact area.
• A widely accepted improvement posits friction force is proportional to the real contact area.
• This hypothesis has underpinned significant research in friction mechanics.

Purpose of the Study:

• To rigorously re-evaluate the relationship between friction force and real contact area.
• To investigate friction behavior during both normal loading and unloading stages.
• To clarify the fundamental origins of friction.

Main Methods:

• In-situ and real-time measurement of friction force.
• Simultaneous measurement of real contact area.
• Experimental procedures conducted during both loading and unloading cycles.

Main Results:

• A consistent linear relationship was observed between friction force and normal load across all stages.
• The relationship between friction force and real contact area demonstrated linearity exclusively during the loading phase.
• Linearity failed to hold for the friction force versus real contact area relationship during the unloading phase.

Conclusions:

• The friction force is invariably proportional to the normal load.
• The widely accepted proportionality between friction force and real contact area is stage-dependent, holding only during loading.
• This finding necessitates a nuanced understanding of friction mechanisms, particularly concerning unloading phenomena.