The fatigue characteristics of the electromechanical and ferroelectric properties of high-displacement RAINBOW (Reduced And INternally Biased Oxide Wafer) actuators were investigated. Rainbows were fabricated from three types of lead-zirconate-titanate-based ferroelectric materials: soft ferroelectrics (PZT-SA and PZT-5H), hard ferroelectrics (PZT-4) and slim-loop ferroelectrics (PLZT 9/65/35). The PZT-4,-5A and-SH compositions were piezoelectric, and PLZT 9/65/35 was electrostrictive. Before fatigue testing, the flexural strength and electromechanical displacement versus load properties were measured for these compositions. Fatigue in the electromechanical displacement properties of Rainbows with increasing number of electric field cycles was observed at low field levels (below the coercive field) under various static loading conditions. For all of the compositions evaluated, actuator free displacement (no load) decreased <10% over 107 electric field cycles. Under 300 g of static load, displacements decreased 20-50% over 107 cycles with PZT-5A and PLZT 9/65/35 exhibiting the least fatigue. The decrease in displacement at high electric field levels (above the coercive field) was measured simultaneously with the degradation of ferroelectric polarization with increasing number of cycles for all compositions except PZT-4. High-field displacements decreased only 7% over 108 cycles for electrostrictive PLZT 9/65/35 Rainbows, whereas the displacements of the piezoelectric PZT-5A and PZT-5H compositions decreased 66% and 43%, respectively. The ferroelectric polarization in PZT-5A and PZT-5H Rainbows fatigued more rapidly than in bulk ceramics of these compositions. PLZT 9/65/35 Rainbows and bulk ceramics exhibited similar fatigue behavior and were more fatigue resistant than PZT-5A and PZT-5H at high fields. The effects of post-fatigue heat-treatment and electrical repoling were also observed.

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The fusion devices currently being developed present several challenges for magnet designers. One challenge lies within the electrical insulation, which must be able to withstand extreme temperatures, large shear and compressive stresses, high operating voltages, and high levels of incident radiation. To address the need for better performing insulation systems, Composite Technology Development (CTD), Inc. has developed CTD-403, a cyanate ester resin with increased radiation resistance, ease of processing and fabrication, low moisture absorption characteristics, and high mechanical and electrical strength at cryogenic and elevated temperatures. The moisture absorption trends of CTD-403/S2 glass composite insulation were studied. The effects of humidity exposure on interlaminar shear strength (ILSS), compressive strength, dielectric strength, and glass transition temperature were also studied. The saturation level of the insulation was seen to increase with the relative humidity of the aging environment. Fickian behavior was seen at room temperatures below 97% relative humidity exposure. Non-Fickian behavior was seen at elevated temperatures. Saturation levels after 6 months exposure were seen to be below typical epoxy-based insulation systems, averaging 0.5% weight gain. Degradation of mechanical and electrical properties was seen with increased humidity exposure and moisture absorption. ILSS showed an average retention rate of 75% after 6 months exposure. The compressive strength showed no decrease after 6 months exposure at room temperature, and show retention rates greater than 90% at 75°C/79% RH. An average dielectric strength of 98.6 kV/mm was seen for all specimens at room temperature (above 90% retention) after 6 months exposure.

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