A comparison of stack load-line (including blocked force and free displacement) as well as dynamic response of two
single crystal PMN-32%PT stacks is provided in this study. The first stack is a 7mm diameter by 0.5mm thickness 60
layer single crystal stack while the second stack is a 6mm diameter by 0.3mm thickness 100 layer single crystal stack.
Blocked force and free displacement measurements were both performed under DC driving conditions. Free
displacement measurements showed that under 500V driving conditions displacements approaching 87&mgr;m (~2500ppm)
and 48&mgr;m (~1450ppm) were obtained for the 6mm and 7mm diameter stacks, respectively. Experimental blocked force
measurements correlated well with theoretical predictions with experimental values approaching 709N and 685N for the
6mm and 7mm diameter stacks, respectively. The error between the theoretical predictions and experimental values was
attributed to the linear load line assumption in the theoretical model whereas the stack stiffness is dependent upon the
applied force. Dynamic measurements performed under a pre-stress of 4MPa indicated an increase in the strain at
frequencies above 500Hz for driving frequencies up to 1000Hz. This was unexpected as the PMN stack resonance was
calculated to be on the order of several kHz.
A -1200 ppm forced volume magnetostriction has been obtained in a [0-3], resin-bonded, Gd5Si2Ge2 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 Gd5Si2Ge2 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, Gd5Si2Ge2 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 Gd5Si2Ge2 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.
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.
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 describes magneto-thermo-mechanical characterization of magnetostrictive composites. The purpose of this study is to evaluate the behavior of magnetostrictive composites under combined magnetic, thermal and mechanical loading, and to determine fundamental properties used for design of actuator and sensor systems that incorporate these materials. Currently the composites are being used in sonar transducers. The magnetostrictive composite contains Terfenol-D (Tb0.3Dy0.7Fe2) particulate embedded into an epoxy binder. Composite form is used due to the relative brittleness and limited operational frequencies of monolithic Terfenol-D. Two different tests were performed both at room temperature and under thermal loading: 1) constant magnetic field with cyclically varying load around a bias load and 2) constant pre-load with varying magnetic field. Testing was performed on five different volume fraction composites, namely, 10%, 20%, 30%, 40% and 50%. Parameters that were evaluated include strain output, magnetic field, magnetization and elastic modulus. Results for the constant magnetic field tests indicate that modulus generally increases with increasing volume fraction and increasing magnetic field. However, for low fields, an initial dip is noticed in modulus (i.e. (Delta) E effect) attributed to domains becoming more mobile at lower magnetic field levels. Results also indicate an increase in modulus with decrease in temperature. Results for the constant load test indicate a strong dependence of strain output on applied pre-stress. Results indicate that max strain peaks at a certain value of the pre-stress and then decreases for increasing pre-stress. Results also indicate that strain output peaks between 0 degree(s)C and +10 degree(s)C and that strain generally increases with increasing volume fraction.