TRW is developing smart structures technology for vibration control in space and automotive applications. Performance verification of composite structures with piezoceramic sensors and actuators in severe mechanical and thermal environments is a key requirement. Graphite epoxy, graphite polycyanate, and graphite thermoplastic members have been fabricated with thin lead zirconate - titanate (PZT, navy types I and II) actuator and sensor wafers embedded in the composite layup. These members were subjected to tension and compression loading, hundreds of cycles of fatigue loading at levels indicative of launch loads, and thermal cycling tests at temperatures found in the hard vacuum of space. Analytic derivations show that the product of PZT modulus and piezoelectric coefficient is a figure of merit for both actuation and sensing. Test results for embedded PZTs are promising, and show correlation with analytic predictions based on vendor material data. Static actuation performance of the type I and II PZTs was found to remain relatively unchanged following static application of tensile strains of up to 600 and 1500 , respectively. A hundred fatigue loading cycles at 60% of these static strain levels were found to cause no degradation in dynamic actuation/sensing performance, while fatigue loading at the 1500 level did cause a degradation of 13%. Twelve thermal cycles over the range C caused a further 13% average degradation in dynamic performance. Dynamic actuation and sensing characteristics were found to vary within the range of over a single temperature cycle. More testing to quantify the results on a statistical basis is indicated, especially for the temperature cycling effects, which were significant.

The performance of the Advanced Composites with Embedded Sensors and Actuators (ACESA) vibration control system is described. The system consists of: three tubular active members sixteen feet long and five inches in diameter, with embedded piezoceramics (PZTs) allowing control of deformation axially and in two bending planes; a 9-channel digitally programmable analog local vibration control electronics unit; and 400 Volt drive electronics for each strut. The system is installed on a space based laser structural simulator at the AF Phillips Lab's Advanced Space Structure Research Experiments (ASTREX) facility at Edwards Air Force Base. The system has demonstrated ability to settle vibrations after a thruster induced slew in 0.2 seconds. Resonant motions generated by reaction wheel torque are attenuated by a factor of 28. Damping is applied to all modes in the frequency range from 10 to 70 Hz, with fundamental modes achieving 20% damping, an increase of two orders of magnitude over the passive damping level. The PZTs used for active damping were also shunted with resistive elements in an attempt to introduce passive damping, although the effect was barely measurable, showing that active damping gives three orders of magnitude better performance than a passive resistive shunt.

TRW has been implementing active damping compensators on smart structures for the past five years.Since that time there have been numerous publications on the use of impedance matching techniques for structural damping augmentation. The idea of impedance matching compensators came about by considering the flow of power in a structure undergoing vibration. The goal of these compensators is to electronically dissipate as much of this flowing power as possible. This paper shows the performance of impedance matching compensators used in smart structures to be comparable to that of active damping compensators.Theoretical comparisons between active damping and impedance matching methods are made using PZT actuators and sensors. The effects of these collocated and non-collocated PZT sensors and actuators on the types of signals they sense and actuate are investigated. A method for automatically synthesizing impedance matching compensators is presented. Problems with implementing broad band active damping and impedance matching compensators on standard Digital Signal Processing (DSP) chips are discussed. Simulations and measurements that compare the performance of active damping and impedance matching techniques for a lightly damped cantilevered beam are shown..

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