Localization in an idealized heterogeneous elastic sheet

Bekele J Gurmessa,Andrew B Croll

doi:10.1039/c6sm01848c

Abstract

Localized deformation is ubiquitous in many natural and engineering materials as they approach failure, and a significant effort has been made to understand localization processes with simple continuum models. Real materials are much more commonly heterogeneous but it is unclear exactly how heterogeneity affects outcomes. In this work we study the response of an idealized heterogenous elastic sheet on a soft foundation as it is uniaxially compressed. The patterned surface layers are created by selective ultraviolet/ozone treatment of the top surface of a polydimethylsiloxane (PDMS) sample using a TEM grid as a mask. By controlling the exposure time of UV/O3, samples ranging from continuous thin films to sets of isolated small plates were created. We find that patterned regions noticeably localize while bulk regions appear as uniform wrinkles, and that local and global strains depend on the pattern pitch, exposure levels and the treatment protocol. Remarkably, various responses can be modeled using well-understood theory that ignores pattern details aside from the small distance between the adjacent boundaries and the local value of strain.

Highlights

Many modern technologies, such as thin film electronics, conformal antennas, structural composites, and self-folding origami and kirigami structures, involve the lamination of a thin film to a substrate which is subjected to various sources of stress.[1–6] While the technologies have created many interesting applied problems, they have motivated fundamental questions regarding precisely what happens to a thin film as it is embedding in three dimensional space
The patterned surface layers are created by selective ultraviolet/ ozone (UV/O3) treatment of the top surface of polydimethylsiloxane (PDMS) using a Transmission Electron Microscopy (TEM) grid as a mask.[24–26]
By controlling the exposure time of UV/O3, samples ranging from continuous thin films to sets of isolated small plates were created

Summary

Introduction

Many modern technologies, such as thin film electronics, conformal antennas, structural composites, and self-folding origami and kirigami structures, involve the lamination of a thin film to a substrate which is subjected to various sources of stress.[1–6] While the technologies have created many interesting applied problems, they have motivated fundamental questions regarding precisely what happens to a thin film as it is embedding in three dimensional space. Many modern technologies, such as thin film electronics, conformal antennas, structural composites, and self-folding origami and kirigami structures, involve the lamination of a thin film to a substrate which is subjected to various sources of stress.[1–6]. A thin film laminated to a semi-infinite soft substrate is a popular model system, largely because of the emergence of a sinusoidal wrinkle pattern when the composite is subject to compression.[7–11]. Several researchers have examined the transition of uniform undulations to localized bending in a homogeneous system (for example, a polymer thin film) on either elastic or fluid substrates as a uniaxial, compressive stress is applied.[12–15]. One of the other features emerging from these models is that the localization process is tied to the boundaries, and the approximation of an infinite sheet is no longer considered reasonable

Methods

Results

Conclusion