Metal-Ceramic Composite Actuators (original) (raw)
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Tailoring the performance of ceramic-metal piezocomposite actuators, ‘cymbals’
Sensors and Actuators A: Physical, 1998
A unique design of metal-ceramic actuators exhibits very high displacement and large generative forces. This new metal-ceramic composite actuator design, the 'cymbal', consists of a piezoelectric disk sandwiched between two truncated conical metal endcaps. The radial motion of the piezoelectric ceramic is converted into flextensional and rotational motions in the metal endcap. Based on previous studies of ceramicmetal composites, a simplified model has been developed to evaluate the properties of cymbals and to aid in materials selection. The influence of the stiffness of the metal, the piezoelectric coefficients of the ceramics and the characteristics of the epoxy bond on actuator performance have been evaluated. It is found that the higher the transverse piezoelectric coefficient, the higher the displacement of the actuator. The stiffness of the metal reduces the displacement but allows the composite to support higher loads. There is a thermally induced displacement of the piezocomposite with the temperature that is related to the thermal expansion mismatch between the metal endcaps and the ceramic. By selecting appropriate materials, it is possible to avoid this thermally induced displacement. Very low or negligible temperature dependence of the displacement is attained by using PZT ceramics with temperature-independent properties together with metal caps having higher Young's modulus and lower thermal expansion coefficients than the ceramics. © 1998 Elsevier Science S.A.
Load characterization of high displacement piezoelectric actuators with various end conditions
Sensors and Actuators A: Physical, 2001
Piezoelectric ceramic transducers are characterized by relatively small strains on the order of 0.1%. One method of achieving signi®cantly larger displacements is to utilize¯exural mode actuators, such as unimorphs or bimorphs. In this paper, we investigate a particular type of stressed unimorph¯exural actuator, viz. the`THUNDER' actuators. (THUNDER TM is a trademark of Face International Corporation). These stressed unimorphs are of interest due to their particularly large¯exural strains. To determine their versatility as high displacement actuators, it was necessary to investigate their actuation capability as a function of load. In addition, our investigation determined that end conditions have an appreciable effect, which has also not been reported in the literature. Therefore, experimental results of the load capabilities of these high displacement actuators with various end conditions are presented here. Commercially available rectangular actuators were chosen for this study. The actuators had been constructed by bonding thin PZT ceramics (0.152 mm thick, 1.37 cm wide, 3.81 cm long) to stainless steel sheets (0.20 mm thick, 1.27 cm wide, 6.35 cm long). They were operated in a¯exural mode. It was shown that progressively restrictive end conditions increased the stiffness, ranging from 2.5 to 23 N/m, enhancing the load capabilities of the actuator. In some cases, displacement actually increased as a function of load. This enhanced stiffness was obtained at a cost of reduced no load¯exural strain (de®ned as the ratio of¯exural displacement and ceramic length), ranging from 1.08% for free-end conditions to 0.2% for highly restricted end conditions. The load bearing capabilities were tested out to 10 N for most end conditions. # 2001 Published by Elsevier Science B.V.
Finite Element Analysis of Piezoelectric Composite Actuators
SAE International Journal of Materials and Manufacturing, 2011
Piezoelectric materials are smart materials that can undergo mechanical deformation when electrically or thermally activated. An electric voltage is generated on the surfaces when a piezoelectric material is subjected to a mechanical stress. This is referred to as the ‘direct effect’ and finds application as sensors. The external geometric form of this material changes when it is subjected to an applied voltage, known as ‘converse effect’ and has been employed in the actuator technology. Such piezoelectric actuators generate enormous forces and make highly precise movements that are extremely rapid, usually in the micrometer range. The current work is focused towards the realization and hence application of the actuator technology based on piezoelectric actuation. Finite element simulations are performed on different types of piezoelectric actuations to understand the working principle of various actuators. The displacements produced by the multilayered actuators are sometimes insufficient compared with the total displacement requirements such as in injector control valve applications in automotive engine environment, therefore it calls for design of an amplification system to increase the stroke using existing multilayered stacks. Thus FE simulation procedures play key role in designing such smart actuating systems. Investigations on various types of displacement amplification systems have been made.
Electromechanical Properties of a Ceramicd31-Gradient Flextensional Actuator
Journal of the American Ceramic Society, 2001
We examined the static axial displacement of a ceramic d 31-gradient flextensional transducer both experimentally and theoretically. Two lead zirconate titanate systems, (PZT)/PZT and PZT/ZnO, were studied. The PZT/PZT transducers consisted of two PZT layers of different d 31 coefficients. The PZT/ZnO transducers consisted of a PZT and a ZnO layer. The PZT/PZT transducers were of an inner-type dome structure. The PZT/ZnO transducers were either flat, or had an inner-or outer-type dome structure by varying the thickness ratio between the two layers or the Sb 2 O 3 content in the ZnO layer. An inner (outer)-type transducer has the large-d 31 layer on the inside (outside) of the dome structure. For the PZT/PZT transducers, the axial displacement varied with the thickness ratio and reached a maximum when the two layers had similar thickness, in agreement with the calculations. With a conductive nonpiezoelectric layer, the PZT/ZnO transducers had higher axial displacements, which varied with the thickness ratio and the Sb 2 O 3 content, than the PZT/PZT transducers. With 6 wt% Sb 2 O 3 , the transducers were flat and the measured displacements at various thickness ratios were similar to the calculated values. With 4 wt% Sb 2 O 3 , the transducers were of an outer type. The measured axial displacements were about twice the calculated values, suggesting an enhanced d 31 value because of the tensile bending stress in the PZT layer. The scaled axial displacements of the PZT/ZnO transducers with 4 wt% Sb 2 O 3 were comparable to that of the Rainbow transducers. With 8 wt% Sb 2 O 3 , the displacements of transducers with thin PZT layers (<0.3 mm) were lower than the calculated values because of increased conductivity in the PZT layer.
Electromechanical Characterization of Bi-based Lead Free Ceramic Multilayer Actuators
Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT), 2013
The electromechanical behaviour of a lead-free ceramic multilayer actuator is described. The actuator is made of a Nd-doped bismuth-alkali-titanate ceramic with inner electrodes of an Ag/Pd-alloy. For electromechanical characterization the actuator is under constant mechanical load and the strain over the applied electric field is recorded. The mechanical load ranges from 0.1 to 80 MPa. The maximum applied electric field is 8 kV/mm. Starting with 0.1 MPa mechanical load the actuator exhibits a maximum strain of less than 0.1%. With increasing load the strain increases up to 0.17 % at 5 MPa. With higher load the strain decreases and reaches 0.125% at 80 MPa. Reducing the mechanical load leads to a steady increase in strain, which results in a doubling of the strain at 0.1 MPa compared to the initial value. The strain characteristic contains an electrostrictive part, a linear piezoelectric regime as well as some creep behaviour.
Journal of Applied Physics, 2014
The electric-field-induced strain response mechanism in a polycrystalline ceramic/ceramic composite of relaxor and ferroelectric materials has been studied using in situ high-energy x-ray diffraction. The addition of ferroelectric phase material in the relaxor matrix has produced a system where a small volume fraction behaves independently of the bulk under an applied electric field. Inter-and intra-grain models of the strain mechanism in the composite material consistent with the diffraction data have been proposed. The results show that such ceramic/ceramic composite microstructure has the potential for tailoring properties of future piezoelectric materials over a wider range than is possible in uniform compositions. V C 2014 AIP Publishing LLC.
Development of Piezoelectric Ceramic Actuators with Graded Porosity
Materials Science Forum, 2003
The objective of this study was to develop bending-type piezoelectric ceramic actuators having functionally graded microstructures (FGM). Porosity-graded lead zirconate titanate (PZT) ceramics were selected as a model material. Miniature porosity-graded actuator samples with three layers of different porosities (0, 10, 20%) were fabricated by sintering layer-stacked powder compacts that consist of PZT and pore-forming agent (PFA) powders in air atmosphere, whereby stearic acid was added as a pore-forming agent. In order to fabricate PZT/Metal or PZT/Polymer FGM actuators using porosity-graded PZT ceramics as a preform, another pore-forming agent, polymethylmethacrylate (PMMA) powder was also used to increase open porosity. The electric-field-induced deflection characteristic of the beam-shaped actuator samples was measured with electric strain gages, and compared with the values calculated from the modified classical laminate theory using the elastic and piezoelectric constants of the non-FGM porous PZT ceramics. It was found that the experimentally measured deflection values of the obtained actuator samples well agreed with the calculated data. An optimum porosity profile that gives the largest deflection was also determined by the modified classical lamination theory. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of the publisher: Trans Tech Publications Ltd, Switzerland, www.ttp.net.