Phase Diagrams of Instabilities in Compressed Film Substrate Systems

Abstract

Subject to a compressive membrane stress, an elastic film bonded on a substrate can become unstable, forming wrinkles, creases or delaminated buckles. Further increasing the compressive stress can induce advanced modes of instabilities including perioddoubles, folds, localized ridges, delamination, and coexistent instabilities. While various instabilities in filmsubstrate systems under compression have been analyzed separately, a systematic and quantitative understanding of these instabilities is still elusive. Here we present a joint experimental and theoretical study to systematically explore the instabilities in elastic filmsubstrate systems under uniaxial compression. We use the Maxwell stability criterion to analyze the occurrence and evolution of instabilities analogous to phase transitions in thermodynamic systems. We show that the moduli of the film and the substrate, the filmsubstrate adhesion strength, the film thickness, and the prestretch in the substrate determine various modes of instabilities. Defects in the filmsubstrate system can facilitate it to overcome energy barriers during occurrence and evolution of instabilities. We provide a set of phase diagrams to predict both initial and advanced modes of instabilities in compressed filmsubstrate systems. The phase diagrams can be used to guide the design of filmsubstrate systems to achieve desired modes of instabilities.