Draping films: a wrinkle to fold transition

Area of Science:

• Materials Science
• Physics
• Mechanics of Materials

Background:

• Polymer films develop wrinkles when subjected to strain from underlying substrates.
• Wrinkle wavelength is determined by material properties and film geometry, particularly thickness.
• At critical strain, wrinkles collapse into folds, localizing stress.

Purpose of the Study:

• To investigate the deformation of an axisymmetric polymer sheet.
• To quantify the force and energy required for fold formation in polymer films.
• To analyze the relationship between film thickness and folding behavior.

Main Methods:

• Experimental examination of an axisymmetric sheet deformation.
• Quantification of the force needed to initiate a fold.
• Analysis of energy scaling with film thickness.

Main Results:

• The energy required to form a single fold scales nearly linearly with film thickness.
• The critical force or displacement for folding scales with film thickness to the four-ninth power.
• Formed folds increase radial stress, reducing the wavelength of remaining wrinkles.

Conclusions:

• The energy balance of the system predicts the observed scaling laws for fold formation.
• Film thickness is a critical parameter governing both the energy and force of folding.
• Folding significantly alters the mechanical response and wrinkling behavior of polymer films.