We prepare a thin (~100 μm) silicone-based elastomer membrane and sputter ultra-thin copper electrodes (16-192 nm) onto each side of the film. Voltages of varying magnitude (1-8 kV) are applied to the electrodes causing an electrostatic pressure to develop which then compresses the elastomer in the through thickness direction. The edges of the membrane are constrained against in-plane expansion, forcing the membrane to deform out of plane. The in-plane strains developed by applying an electric field are characterized by measuring the stiffness of the membrane via indentation at different applied voltages. Closed-form solutions for membrane deflection are used with the experimental measurements to determine the relationship between the modulus of the cracked electrode/elastomer multi-layer and the electrically induced in-plane strain. Analytical models predicting the relationship between electrode crack spacing, layer properties, and effective modulus of the multi-layer are presented. Building on the knowledge gained from the membrane experiments, uni- axial tension specimens of an electrode/elastomer multi-layer are tested and preliminary results discussed.
Commercial applications of micro-electromechanical systems (MEMS) continue to be plagued by reliability issues encountered during fabrication and operation. One of the most prevalent problems is the adhesion between adjacent components since adhesive forces are known to promote wear and defect-related failures. In extreme circumstances, the adhesion is large enough to prevent separation, a phenomenon commonly referred to as stiction-failure. The objective of current work is to determine analytically whether dynamic excitation may be used to repair stiction-failed cantilevers. This is accomplished by relating the structural dynamic response to the de-cohesion of stiction-failed micro-cantilever beams under various loading conditions.
SIMS has developed a simple means for detecting and monitoring both absolute and relative clamp load, or bolt tension, in fastener systems. More than twenty-five percent of automotive failures are known to be due to undetected loss of fastener clamp load. While the equivalent aerospace maintenance statistics are not known, the average automobile has 3,500 fasteners while a Boeing 747 has closer to one million. It is therefore anticipated that the new SensaBolt clamp load tracking system could find wide applications in the aerospace arena. We describe a visually-evident and retrofitted clamp load monitoring design which is based on the differential joint substrate compression at, and immediately adjacent to, the fastener location. This intrinsically-accurate indicator does not necessarily require alteration in either the bolt or nut geometries, thereby facilitating product introduction and retrofit in aging aircraft applications. In addition, SensaBolt's sole reliance on substrate compression renders it more accurate then torque wrench or turn-of-nut techniques. Readout may be accomplished by any of three principal methods: for those applications with ease of access to the sensor, loss of tension can be determined by direct visual inspection. Application of a standard wrench can then be made to restore the fastener's proper tightness, per the SensaBolt indicators. In those instances where line-of-sight is unimpeded and more formal inspection is desired, the SensaBolt may be interrogated by a laser scanner bar code reader. Finally, SensaBolt may be addressed by the SIMS fiber optic harness for those instances where full-time remote interrogation is desired.
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