The development of a novel piezoelectric induced-strain actuator possessing an innovative internal amplifying structure is presented in this paper. This actuator basically consists of a metal frame and two lead zirconate titanate (PZT) piezoelectric ceramic patches. The metal frame is bent to form an open trapezoid, where its center part has a specially designed saddle-like unit and its slanting legs are attached with PZT patches. The saddle-like unit has an amplifying-lever mechanism at the corners to increase the displacement output of the whole actuator even its legs are mechanically clamped. When an electric field is applied across the thickness of the PZT patches, the patches induce deformations on the whole actuator through the piezoelectric <i>d<sub>31</sub></i> effect. The saddle-like unit can relax the constraints at the joints between the unit and the legs by stretching itself during bending. Piezoelectric finite element analysis is used to maximize the work output of displacement and blocked force of the actuator under different geometric parameters. The results are in good agreement with those obtained from quasi-static measurements, showing that the actuator has work output comparable to and larger than the existing induced-strain actuators (e.g., THUNDER) under fixed mounting conditions. Therefore, the actuator has great potential for use in various practical smart structures and integrated systems, including active-passive vibration isolation and micro-positioning.
A novel tunable mass damper (TMD) is developed using the sensitivity of transversal bending stiffness and resonance frequencies of a beam to its axial force. This smart TMD consists of a force actuator-sensor unit suspended in a rigid frame by two flexible beams coupled to the axial ends of the unit and the frame. The force actuator-sensor unit is composed of a giant magnetostrictive composite-based force actuator for producing an axial force to the beams and a pair of piezoelectric ceramic-based force sensors for generating a tuning signal. Through adjusting the magnetic field strength applied to the force actuator to change the axial force exerted on the beams, the transversal bending stiffness of the beams and hence the natural frequency of the smart TMD is tuned. In this paper, the design, fabrication, and characterized of the smart TMD is described. The measured resonance frequency of the smart TMD is 65 Hz at zero magnetic tuning field and 50 Hz at an applied magnetic field of 686 Oe. Tunability of the resonance frequency as high as 23 % is achieved with the reasonably low magnetic tuning field. The frequency response functions as measured using the force sensors agree well with those obtained using a commercial accelerometer, indicating a great possibility of directly deploying the force sensors for active or semi-active tuning or control purposes.
A -1200 ppm forced volume magnetostriction has been obtained in a [0-3], resin-bonded, Gd<sub>5</sub>Si<sub>2</sub>Ge<sub>2</sub> particulate composite. The strain is a result of a magnetically induced phase transformation from a high volume (high temperature, low magnetic field) monoclinic phase to a low volume (low temperature, high magnetic field) orthorhombic phase. The particles used in the composite were ball-milled from a bulk sample and sieved to obtain a size distribution of ≤600 mm. Bulk Gd<sub>5</sub>Si<sub>2</sub>Ge<sub>2</sub> was manufactured via arc melting and subsequently annealed at 1300°C for 1 hour to produce a homogenous, polycrystalline sample. The transformation temperatures of the bulk sample, as measured using a Differential Scanning Calorimeter (DSC), were Ms = -9.3°C, Mf = -14.6°C, As = -4.4°C, and Af = -1.2°C. The composite and the bulk samples were magnetically characterized using a SQUID magnetometer, and found to undergo a paramagnetic to ferromagnetic transition during the phase transformation, consistent with published results. The bulk sample was also found to possess a maximum linear magnetostriction of -2500 ppm.
A -1300ppm strain has been obtained in a [0-3], resin binder, Gd<sub>5</sub>Si<sub>2</sub>Ge<sub>2</sub> particulate composite. The strain is a result of a temperature induced phase transformation from a high volume (high temperature, low magnetic field) monoclinic phase to a low volume (low temperature, high magnetic field) orthorhombic phase. The particles used in the composite were ball-milled from a bulk sample and were sieved to obtain a size distribution of <600micron. Bulk Gd<sub>5</sub>Si<sub>2</sub>Ge<sub>2</sub> was manufactured via arc melting and subsequently annealed at 1300°C for 1 hour to produce a textured, polycrystalline sample. The transformation temperatures of the bulk sample, as measured using a Differential Scanning Calorimeter (DSC), were Ms=-9.3°C, Mf=-14.6°C, As=-4.4°C, and Af=-1.2°C. The bulk sample was magnetically characterized using a SQUID magnetometer, and found to undergo a paramagnetic to ferromagnetic transition during the phase transformation, consistent with published results. The bulk sample was also found to possess a -8000ppm volume magnetostriction, agreeing well with measured unit cell parameters of the different phases.
The development of a piezoelectric hydraulic pump with innovative active valves is presented in this study. The pump structure basically consists of a diaphragm type piezoelectric stack actuator and two specially designed unimorph disc valves acting as inlet and delivery valves. Static and dynamic piezoelectric finite element analyses were used to maximize the delivered fluid volume per stroke and to predict the resonance characteristics of the pump, respectively. A structural optimization technique was performed to optimize the efficiency of the pump versus its geometrical dimensions. A transient CFD model was used to predict flow rates. Dynamic experiments were also conducted and results are in good agreement with those obtained from the simulation.
A 15 percent nickel composite was manufactured and tested under a sinusoidally applied magnetic field at a frequency of 0.3 Hz around a DC bias of 0kA/m without an external mechanical load. The particulate are obtained from a process known as spark erosion, resulting in particulate that are nearly spherical in shape. Parameters that were recorded include strain, magnetic field, and magnetic flux. Experimental strain output values were comparable to strain measured from a single crystal nickel along the axis. However, the effects of the epoxy are non-negligible and results regarding texturing of the composite are inconclusive.
This paper presents an experimental investigation of the dynamic behavior of a 1-3 type magnetostrictive composite, with emphasis on the evaluation of fundamental material properties pertinent to device design. The fabricated 1-3 magnetostrictive composite comprises 51 percent volume fraction of Terfenol-D particulates embedded and magnetically aligned in a passive epoxy matrix. The dynamic magnetomechanical properties of the composite are measured as functions of bias field, drive field, and frequency. These properties include Young's moduli at constant magnetic field strength (EH3) and at constant magnetic flux density (EB3), magnetomechanical coupling coefficient (k33), dynamic relative permeability (ur33), dynamic strain coefficient (d33), mechanical quality factor (Qm), and the ratio of the dynamic strain coefficient to the dynamic susceptibility. Dependence of material properties on applied fields and frequency is observed with no evidence of eddy current losses. The observed eddy current effect agrees with the prediction of classical eddy current theory. This suggests that the composite can provide superior high-frequency performance as compared to monolithic Terfenol-D and laminated Terfenol-D systems. Implications for high-frequency applications of the material to resonance devices are also described.