Super-Flexible Sensors and Advanced 3D Morphing Actuators based on Elastic Instability

Wang, Cong (2020) Super-Flexible Sensors and Advanced 3D Morphing Actuators based on Elastic Instability. Doctoral thesis, Northumbria University.

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Abstract

Super-flexible devices based on soft materials have the potential to sustain large mechanical deformations, enabling advanced applications such as flexible electronics, soft robots, artificial skin, and biomedical transducers. Subject to a large compression, materials may undergo different types of elastic instabilities such as wrinkles, creases, and folds. Despite recent growing interests in turning this usually unwanted phenomenon into useful engineering applications (e.g. tactile sensing), this topic remains relatively under-researched.
Therefore, this thesis focuses on developing the control mechanisms of elastic instabilities, and their applications in sensing and actuation systems.

Elastic instabilities induced strain-gated logic sensing technology is developed by research into micro structured metal-elastomer tri-layer system. The test structures are designed to study the deformation behaviour and to exploit the large strain sensing mechanism. The stepwise electrical signals are achieved (from ~1010 to ~120 Ω at first switching stage and then to ~50 Ω at second switching stage) that survived much higher than usual compressive strains of up to 60%.

On the other hand, elastic instabilities induced topo-optical sensing strategy is created by patterning microstructure arrays within the tri-layer system. Two unwanted phenomena (creases/folds and oxygen quenching effect) are turned into a responsive and programmable 'fold to glitter' function through micro engineering, which can light up areas of an object or material by creating microscopic creases/folds within its surface. The signal-Noise-Ratio (SNR) contrast in optical pattern generation is improved by 6 folds due to the oxygen quenching effect. The numerical analysis by ABAQUS provides the fundamental theory on the mechanism of generating targeted folding through simulating the in-plane and out-of-plane strain energy localization.
Different luminescent optical patterns are demonstrated under in-plane uniaxial or equi-biaxial compression.

Apart from the surface deformation, the bulk deformation of heterogeneous layered structures of soft functional hydrogel is also developed to generate the controllable and reconfigurable 3D morphing device. The initial configurations with various shapes (“S”, “W” and “C”) are demonstrated due to the swelling ratio mismatch. The developed sensing and actuation technologies provide opportunities for future applications in flexible electronics, tuneable optics, soft robotics and bio-medical systems.

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