Frictional strength regulated by roughness alignment

Area of Science:

• Tribology
• Materials Science
• Physics of Interfaces

Background:

• Rough surfaces are common in natural and engineered systems.
• The relationship between roughness alignment and friction is not fully understood.

Purpose of the Study:

• Investigate how roughness alignment affects friction and stick-slip transitions.
• Quantify the influence of roughness matching on frictional behavior.

Main Methods:

• Controlled rotation of one surface relative to another to vary roughness alignment.
• Measurement of static friction coefficient and micromechanical quantities.
• Statistical analysis of microcontact properties and introduction of the contact fabric tensor.

Main Results:

• Achieved an order-of-magnitude variation in maximum static friction coefficient by controlling roughness alignment.
• Demonstrated that roughness alignment governs both the amplitude and angular range of frictional strength variation.
• Identified universal statistical patterns in microcontact area, orientation, and deformation under shear, following extreme value distributions.
• Introduced the contact fabric tensor as a predictor for friction and sliding onset.

Conclusions:

• Roughness alignment is a critical factor in determining frictional behavior at interfaces.
• The contact fabric tensor provides a unified measure for roughness matching and friction prediction.
• Findings enhance understanding of friction and inform designs in mechanics, adhesion, and geophysics.