W. Keats Wilkie

Anisotropic Laminar Piezocomposite Actuator Incorporating Machined PMN–PT Single-crystal Fibers

The design, fabrication, and testing of a flexible, laminar, anisotropic piezoelectric composite actuator utilizing machined PMN–32%PT single-crystal fibers is presented. The device consists of a layer of rectangular single-crystal piezoelectric fibers in an epoxy matrix, packaged between interdigitated electrode polyimide films. Quasistatic freestrain measurements of the single-crystal device are compared with measurements from geometrically identical specimens incorporating polycrystalline PZT-5A and PZT-5H piezoceramic fibers. Free-strain actuation of the single-crystal actuator at low bipolar electric fields (±250 V/mm) is ≈400% greater than that of the baseline PZT-5A piezoceramic device, and ≈200% greater than that of the PZT-5H device. Free-strain actuation under high unipolar electric fields (0–4 kV/mm) is 200% of the PZT-5A baseline device, and 150% of the PZT-5H alternate piezoceramic device. Performance increases at low field are qualitatively consistent with predicted increases based on scaling the low-field d33 piezoelectric constants of the respective piezoelectric materials. High-field increases are much less than scaled d33 estimates, but appear consistent with high-field free-strain measurements reported for similar bulk single-crystal and piezoceramic compositions. Measurements of single-crystal actuator capacitance and coupling coefficient are also provided. These properties were poorly predicted using scaled bulk material dielectric and coupling coefficient data. Rule-of-mixture calculations of the effective elastic properties of the single-crystal device and estimated actuation work energy densities are also presented. Results indicate longitudinal stiffnesses significantly lower (50% less) than either piezoceramic device. This suggests that single-crystal piezocomposite actuators will be best suited to low induced-stress, high strain, and deflection applications.

Nonlinear Response of the Macro Fiber Composite Actuator to Monotonically Increasing Excitation Voltage

A nonlinear model for a piezoelectric continuum subjected to a monotonic increase in electric field under constant mechanical load is investigated. A general model is derived and then specialized for a piezoceramic-based material with anisotropic actuation and mechanical properties, for example, the Macro Fiber Composite (MFC) actuator. This formulation includes the linear-elastic mechanical response, as well as linear and second-order piezoelectric behavior and a second-order electromechanical cross-term. Using previously published work by the same authors (Williams, R.B., Inman, D.J. and Wilkie, W.K. 2004. “Tensile and Shear Behavior of Macro Fiber Composite Actuators,” Journal of Composite Materials, 38(10):855—870) dealing with the mechanical response of the MFC, this set of material properties is determined experimentally in order to characterize the response of this device to given external loading conditions.

Control of a Space Rigidizable Inflatable Boom Using Macro-fiber Composite Actuators

An experimental investigation of vibration testing and active control of a space rigidizable inflatable composite boom containing embedded piezoelectric composite actuators was conducted. Inflatable deployable space structures offer reduced mass, higher packaging efficiency, lower life cycle cost, simpler design with fewer parts, and higher deployment reliability for many large deployable spacecraft structures applications. Enhancing deployed precision and repeatability for these structures is an ongoing research area, in particular for rigidizable inflatable material systems. In this study, in situ vibration testing and active damping using piezoelectric macro-fiber composite actuators embedded within a typical space-rigidizable deployable composite boom are investigated The embedded macro-fiber composites are shown to be capable of surviving integration, packaging, deployment and thermal rigidization in vacuum, and subsequently operating at their full actuation capability. Positive position feedback controllers using accelerometer, laser vibrometer, and strain gage feedback signals are designed and experimentally evaluated. Velocity-proportional and acceleration-proportional controllers are shown to be capable of attenuating fundamental bending response significantly using only modest control authority (—23dB with 10% of available voltage).

Design and Manufacturing of a Model-scale Active Twist Rotor Prototype Blade

The design and manufacturing of an active twist rotor blade for vibration reduction in helicopters are presented. The rotor blade is integrally twisted by direct strain actuation through embedded piezoelectric fiber composite actuators distributed along the span of the blade. Highlights of the analysis formulation used to design this type of active blade are presented. The requirements for the prototype blade, along with the final design results are also presented. Detailed aspects of its manufacturing are described. Experimental structural characteristics of the prototype blade compare well with design goals, and bench actuation tests characterize its basic actuation performance. The design and manufacturing processes permit the realization of an active blade that satisfies a given set of design requirements. This is used to later develop a fully active rotor blade system.

TEMPERATURE-DEPENDENT THERMOELASTIC PROPERTIES FOR MACRO FIBER COMPOSITE ACTUATORS

This research effort models the thermoelastic properties of the macro fiber composite actuator as a function of temperature. The required temperature-dependent properties of each constituent material are obtained, and the orthotropic layer properties are calculated using a variety of micromechanics models, with the most accurate being selected based on a comparison with ANSYS finite element models. Equations for the four independent stiffness parameters and two coefficients of thermal expansion of the entire actuator are derived using a classical lamination approach. These results agree closely with an ANSYS finite element model of the unit cell of the macro fiber composite actuator.

Rotorcraft Aeroelastic Testing in the Langley Transonic Dynamics Tunnel

Wind-tunnel testing of a properly scaled aeroelastic model helicopter rotor is considered a necessary phase in the design and development of new rotor systems. For this reason, extensive testing of aeroelastically scaled model rotors is done in the Transonic Dynamics Tunnel (TDT) located at the Langley Research Center. A unique capability of this facility, which enables proper dynamic scaling, is the use of diflourodichloromethane, or Refrigerant-12 (R-12) as a test medium. The paper presents a description of the TDT and a discussion of the benefits of using R-12 as a test medium. A description of the system used to conduct model tests is provided and examples of recent rotor tests are cited to illustrate the types of aeroelastic model rotor tests conducted in the TDT.

Active-Twist Rotor Control Applications for UAVs

Abstract : The current state-of-the-art in active-twist rotor control is discussed using representative examples from analytical and experimental studies, and the application to rotary-wing UAVs is considered. Topics include vibration and noise reduction, rotor performance improvement, active blade tracking, stability augmentation, and rotor blade de-icing. A review of the current status of piezoelectric fiber composite actuator technology, the class of piezoelectric actuators implemented in active-twist rotor systems, is included.

Control of a Space Rigidizable-Inflatable Boom Using Embedded Piezoelectric Composite Actuators

An experimental investigation of vibration testing and active control of a space rigidizable inflatable composite boom containing embedded piezoelectric composite actuators was conducted. Inflatable deployable space structures offer reduced mass, higher packaging efficiency, lower life cycle cost, simpler design with fewer parts, and higher deployment reliability for many large deployable spacecraft structures applications. Enhancing deployed precision and repeatability for these structures is an ongoing research area; in particular, for rigidizable inflatable material systems. In this study we demonstrate in situ vibration testing and active damping using piezoelectric Macro- Fiber Composite actuators embedded within a typical space-rigidizable deployable composite boom. The embedded Macro-Fiber Composite are shown to be capable of surviving integration, packaging, deployment and thermal rigidization in vacuum, and subsequently operating at their full actuation capability. Positive position feedback controllers using accelerometer, laser vibrometer, and strain gage feedback signals are designed and experimentally evaluated. Velocity-proportional and acceleration proportional controllers shown to be capable of attenuating fundamental bending response significantly using only modest control authority (-23dB with 10% of available voltage).