Abstract
Metal-elastomer interfacial systems, often encountered in stretchable electronics, demonstrate remarkably high interface fracture toughness values. Evidently, a large gap exists between the rather small adhesion energy levels at the microscopic scale (‘intrinsic adhesion’) and the large measured macroscopic work-of-separation. This energy gap is closed here by unravelling the underlying dissipative mechanisms through a systematic numerical/experimental multi-scale approach. This self-containing contribution collects and reviews previously published results and addresses the remaining open questions by providing new and independent results obtained from an alternative experimental set-up. In particular, the experimental studies on Cu-PDMS (Poly(dimethylsiloxane)) samples conclusively reveal the essential role of fibrillation mechanisms at the micro-meter scale during the metal-elastomer delamination process. The micro-scale numerical analyses on single and multiple fibrils show that the dynamic release of the stored elastic energy by multiple fibril fracture, including the interaction with the adjacent deforming bulk PDMS and its highly nonlinear behaviour, provide a mechanistic understanding of the high work-of-separation. An experimentally validated quantitative relation between the macroscopic work-of-separation and peel front height is established from the simulation results. Finally, it is shown that a micro-mechanically motivated shape of the traction-separation law in cohesive zone models is essential to describe the delamination process in fibrillating metal-elastomer systems in a physically meaningful way.
Highlights
Close integration of micro-electronic devices with biological tissue would facilitate a realm of ground-breaking applications: from surgical and diagnostic implements that naturally integrate with the human body, such as eye-implanted retina-shaped photo-sensor arrays, electrode array probes for deep brain, heart, or nerve stimulation, chips and sensors on the tip of minimally invasive instruments, and cardiac diagnostics, to numerous ex-vivo applications, such as sensory skin for robotics and prostheses and wearable health monitoring e.g., [1,2,3,4,5,6,7,8,9]
Klein et al [12] propose qualification test methods designed for stretchable electronics, which result in several failure modes that closely resemble the actual device
The maximum difference in these strain fields was less than 10% from which it was concluded that the model adequately describes the mechanics of the peel test for this particular material system at the macroscopic and mesoscopic scale
Summary
Close integration of micro-electronic devices with biological tissue would facilitate a realm of ground-breaking (in-body) applications: from surgical and diagnostic implements that naturally integrate with the human body, such as eye-implanted retina-shaped photo-sensor arrays, electrode array probes for deep brain, heart, or nerve stimulation, chips and sensors on the tip of minimally invasive instruments, and cardiac diagnostics, to numerous ex-vivo applications, such as sensory skin for robotics and prostheses and wearable health monitoring e.g., [1,2,3,4,5,6,7,8,9]. (c) the fibrils at meso-scale; (d) a fibril at micro-scale This contribution aims to unravel the huge gap that exists between the microscopic adhesion energy and the macroscopic WOS of the aforementioned Cu-PDMS systems by means of a multi-scale experimental and numerical analysis. To this end, the key results from a range of previously-reported, experimental and numerical studies are collected and reviewed, while addressing the remaining open questions through enriching the analysis by newly designed, fully independent, micro-tests to come to a consistent, self-containing, overall description of the multi-scale fibrillation process. It is shown that a micro-mechanically motivated shape of the traction-separation law used in the CZ model is essential to describe the delamination process in fibrillating metal-elastomer systems in a physically meaningful way
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