| Textile Capacitor |
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| Oct 01 2006 | |
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Page 3 of 4
Advertisement: In the future, superior dielectrics that offer improved structural and electrical performance will increase the structure’s energy density storage capacity. The AFRL team is working with researchers from the University of Dayton Research Institute (UDRI) to develop highperformance resins for achieving dielectric performance with good structural properties. This work involves doping resins to improve the voltage breakdown strength, provide low electromagnetic losses, and increase the material dielectric constant. In addition, the team is developing material that is compatible with the injected structural resin and also has low moisture uptake, since the dielectric is not hermetically sealed. The researchers are synthesizing this resin material for use in the precision dielectric coating pultrusion process that AFRL is currently developing to produce the next generation of coaxial structural capacitors. Figure 2 shows a scanning electron microscope image of the doped resin. Researchers have also made significant progress in lowering the structural capacitor concept’s specific weight and improving its durability. The first improvement was in eliminating the copper paint electrode. This step involved thorough consideration of several options, including metal foil bonding, electroless plating, metal coating flame spray, vapor deposition, and braiding of a conductive surface with composite fibers. For the second-generation device, researchers used a conductive fiber overbraid to improve structural and electrical performance. They tested several varieties of this overbraid, including variations fabricated from titanium, copper zirconium alloy, and carbon tow. These braids provided an overall thickness of approximately 4 mils, enabling a small profile for integration into the composite architecture. Researchers evaluated these materials based on cost, electrical resistance, weight, and ease of fabrication, ultimately choosing the carbon braid electrode (see Figure 3) for future development activity. The team also evaluated copper zirconium options for the center electrode. Although the zirconium contained in the copper improved structural fatigue resistance with minimal impact to electrical conductivity, the desire to further reduce weight has since inspired additional efforts to fabricate the center electrode using carbon fiber tow in a pultrusion process. Finally, researchers used the Textile Composite Analysis for Design (TEXCAD) computer program to model the plain weave unit cell structure used in the feasibility study. TEXCAD is a general-purpose micromechanics code that models yarn architecture to predict three-dimensional thermal and mechanical properties, damage initiation and progression, strength under tension, compression, and shear. These analyses guided the development of an advanced textile architecture and resulted in a new weave that provided significant fiber volume fraction increase and improved weight efficiency. Researchers then worked with the UDRI team to model this new weave using a novel finite element approach in ABAQUS, a finite element analysis software suite that uses embedded elements. ABAQUS’ embedded elements enabled detailed modeling of the complex architecture, which established mechanical performance estimates that the team will use to baseline empirical results and update vehicle conceptual design application studies. In addition, the researchers performed preliminary analyses characterizing the Lorentz forces induced during structural capacitor system discharge. These forces arise from electrostatic and electromagnetic fields and can induce significant mechanical stresses in the dielectric layers. The team’s parametric studies characterized both physical and operational effects on the stress levels induced into the dielectric material. |
