Unconventional Localization Prior to Wrinkles and Controllable Surface Patterns of Film Substrate Bilayers Through Patterned Defects in Substrate

TL;DR

This paper introduces a bilayer system with patterned substrate defects that enables unconventional surface pattern transitions under compression, allowing for engineered diverse surface topologies.

Contribution

It demonstrates how patterned substrate defects can control and induce unique surface pattern transitions, expanding the possibilities for surface engineering.

Findings

Defects trigger local ridges and folds at low strains.

Phase transition from wrinkles to folds is reversed by defects.

Diverse surface patterns can be engineered by varying defect parameters.

Abstract

A novel bilayer is introduced, consisting of a stiff film adhered to a soft substrate with patterned holes beneath the film and substrate interface. To uncover the transition of surface patterns, two dimensional plane strain simulations are performed on the defected bilayer subjected to uniaxial compression. Although the substrate is considered as the linear elastic material, the presence of defects can directly trigger the formation of locally ridged and then folding configurations from flat surface with a relatively small compressive strain. It is followed by the coexisting phases of folds and wrinkles under further overall compression. This phase transition reverses the traditional transition of wrinkle to ridge or fold for defect free substrates. It is also found that the onset of initial bifurcation is highly dependent on the spatial configuration and geometries of holes, since the interaction of defects allows more strain relief mechanisms beyond wrinkling. Furthermore, a rich diversity of periodic surface topologies, including overall waves, localizations, saw like and coexisting features of folds and wrinkles can be obtained by varying the diameter, depth and spacing of holes as well as compressive strain, which provides a potential approach to engineer various surface patterns for applications.