Adhesion-induced fingering instability in thin elastic films under strain

Area of Science:

• Materials Science
• Physics
• Mechanics of Materials

Background:

• Adhesive contact mechanics is crucial for understanding material interfaces.
• Elastic film deformation under indentation can lead to complex pattern formation.
• The influence of pre-strain on adhesive contact instabilities is not fully understood.

Purpose of the Study:

• To investigate the formation of adhesive fingers in thin elastic films during contact.
• To analyze the effect of uniaxial pre-strain on the resulting fingering patterns.
• To develop a model explaining the anisotropic behavior of the fingering instability.

Main Methods:

• Indentation experiments using a spherical glass indenter on thin elastic films.
• Controlled application of uniaxial pre-strain to the elastic films.
• Optical microscopy to observe and characterize the fingering patterns.
• Quantitative analysis of pattern anisotropy and wavelength.

Main Results:

• Adhesive fingers spontaneously emerge at the contact periphery with a characteristic wavelength.
• Uniaxial pre-strain induces anisotropic fingering patterns aligned with the strain axis.
• The transition from isotropic to anisotropic patterning was quantitatively characterized.
• A simple model successfully captured the origin of the observed anisotropy.

Conclusions:

• The study reveals a novel mechanism for pattern formation in adhesive contact.
• Pre-strain offers a method to control the anisotropy of elastic instabilities.
• The developed model provides fundamental insights into the mechanics of adhesive instabilities in strained films.