and force distributions. Experimental details of the associated deformation response are quantified in real-time using Digital Image Correlation (DIC). Output from the sensor array can be related to shape and force distributions by solving the nonlinear inverse problem using a novel Singular Value Decomposition (SVD) method. 8.2 Research Approach and Results The current research approach consists of the following. (a) Fabrication of multifunctional robotic structures with integrated electronic components. (b) Design of experiments for characterizing the mechanics of multifunctional robotic structures using load cells and 3D Digital Image Correlation. (c) Experimental characterization of loads and deformations of multifunctional robotic structures for enhancement of new FEA models for compliant multifunctional robotic structures. 8.2.1 Fabrication of Multifunctional Robotic Structures We have developed elastomeric electrodes and strain gauges (latex, PDMS, or other elastomeric host polymers loaded with exfoliated graphite) that can be painted onto surfaces (Fig. 8.1). The exfoliation of graphite results in an electrically conductive mixture of graphene and somewhat thicker sheets/flakes of graphite. Mixing the exfoliated graphite (EG) into an elastomeric host produces a conductive composite. The electrical conductivity and the Young’s modulus of the composite depend on the amount of EG in the host (the loading), as well as the deformation of the material. Previously, we have investigated similar composites based on carbon nanotubes (CNTs), and have begun looking at the thermal response of these materials as well. The composites can be applied by spray-coating, brush coating, printing, casting, etc., allowing them to be placed in multiple locations on a deformable surface, such as the small wing of our test-bed. These materials have high gauge factors (change in resistance with strain), yet still maintain a low Young’s modulus. The former gives them the high sensitivity required for these applications, while the latter makes the sensor more compliant than the wing material in order not to interfere with the movement of the compliant structure. Traditional strain gauges, such as the metal foil type, do not have the large strain capabilities of these elastomeric composites, nor the necessary compliance, nor the scalability. Fig. 8.1 (Top) Schematic illustration of separation of the layers in graphite by exfoliation, SEM images of exfoliated graphite (EG) showing mixtures of sheets of graphene and multi-layer graphite, and latex strain sensors. (Center) Deposition and patterning by spray coating through a stencil. (Bottom) Compliant electrode/sensor material on a compliant substrate 60 H.A. Bruck et al.
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