Fracture, delamination, and buckling of elastic thin films on compliant substrates

Abstract

A series of studies have been conducted for mechanical behavior of elastic thin films on compliant substrates. Under tension, the film may fracture by growing channel cracks. The driving force for channel cracking (i.e., the energy release rate) increases significantly for compliant substrates. Moreover, channel cracking may be accompanied by interfacial delamination. For a film on a relatively compliant substrate, a critical interface toughness is predicted, which separates stable and unstable delamination. For a film on a relatively stiff substrate, however, a channel crack grows with no delamination when the interface toughness is greater than a critical value. An effective energy release rate for the steadystate growth of a channel crack is defined to account for the influence of interfacial delamination on both the fracture driving force and the resistance, which can be significantly higher than the energy release rate assuming no delamination. Alternatively, when the film is under compression, it tends to buckle. Two buckling modes have been observed, one with interfacial delamination (i.e., buckle-delamination) and the other without delamination (i.e., wrinkling). By comparing the critical stresses for the onset of buckling, we give a criterion for the selection of the buckling modes, which depends on the stiffness ratio between the film and the substrate as well as the interface defects. A general conclusion from these studies is that, whether tension or compression, the interfacial properties are critical in controlling the morphology and failure of elastic thin films on compliant substrates.

Delamination Behavior of Highly Stretchable Soft Islands Multi-Layer Materials

“…The majority of applied strains are accommodated by fopening of the cracks and stretching of the soft islands, so the rest of the hardened surface is shielded from straining and further uncontrolled cracking [12,13]. However, cracks in multi-layer composites may, as all discontinuities or imperfections, be the starting point for damage to the layers or delamination between layers [24,25]. In the considered setup, two types of damage are possible: (a) pre-formed cracks in the hardened surface destabilize and propagate further into the soft islands or the soft PDMS below, or (b) the conducting silver layer delaminates from the hardened PDMS.…”

Strain engineered domain structure and their relaxation in perpendicularly magnetized Co/Pt deposited on flexible polyimide

“…Thus wrinkle formation might be excluded within the applied range of compressive strain in our case. It is known that buckling of a stiff film deposited upon elastic substrate can occur at lower strain values depending on morphology of substrate, presence of localized artefacts as well as the adhesion strength between the film and substrate [31][32][33]. The PI substrate used in our case is elastic in nature.…”