Mechanical validation of smart structures

Abstract

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.