• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.8
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• pp.870-879
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• 2007

In this study, various damage modes in bending unimorph piezoelectric composite actuators with a thin sandwiched PZT plate during bending fracture tests have been evaluated by monitoring acoustic emission (AE) signals in terms of waveform and peak frequency as well as AE parameters. Three kinds of actuator specimens consisting of woven fabric fiber skin layers and a PZT ceramic core layer are loaded with a roller and an AE activity from the specimen is monitored during the entire loading using an AE transducer mounted on the specimen. AE characteristics from a monolithic PZT ceramic with a thickness of $250{\mu}m$ are examined first in order to distinguish different AE signals from various possible damage modes in piezoelectric composite actuators. Post-failure observations and stress analyses in the respective layers of the specimens are conducted to identify particular features in the acoustic emission signal that correspond to specific types of damage modes. As a result, the signal classification based on waveform and peak frequency analyses successfully describes the failure process of the bending piezoelectric composite actuator exhibiting diverse failure mechanisms. Furthermore, it is elucidated that when the PZT ceramic embedded actuators are loaded mechanical bending loads, the failure process of actuator specimens with different lay-up configurations is almost same irrespective of their lay-up configurations.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.8
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• pp.880-888
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• 2007

This article describes the load capability of bending piezoelectric actuators with a thin sandwiched PZT plate in association with the stored elastic energy induced by an increased dome height after a curing process. The stored elastic energy within the actuators is obtained via a flexural mechanical bending test. The load capability is evaluated indirectly in terms of an actuating displacement with a load of mass at simply supported and fixed-free boundary conditions. Additionally, a free displacement under no load of mass is measured for a comparison with an actuating displacement. The results reveal that an actuator with a top layer having a high elastic modulus and a low coefficient of thermal expansion exhibits a better performance than the rest of actuators in terms of free displacement as well as actuating displacement due to the formation of the large stored elastic energy within the actuator system. When actuators are excited at AC voltage, the actuating displacement is rather higher than the free displacement for the same actuating conditions. In addition, the effect of PZT ceramic softening results in a slight reduction in the resonance frequency of each actuator as the applied electric field increases. It is thus suggested that the static and dynamic actuating characteristics of bending piezoelectric composite actuators with a thin sandwiched PZT plate should be simultaneously considered in controlling the performance.

• Macromolecular Research
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• v.17 no.2
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• pp.116-120
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• 2009

The cellulose smart material called electro-active paper (EAPap) is made by regenerating cellulose. However, the actuator performance is degraded at low humidity levels. To solve this drawback, EAPap bending actuators were made by activating wet cellulose films in three different room-temperature ionic liquids: l-butyl-3-methylimidazolium hexaflurophosphate ($BMIPF_6$), 1-butyl-3-methylimidazolium chloride (BMICL) and 1-butyl-3-methylimidazolium tetrafluroborate ($BMIBF_4$). In the results, the actuator performance was dependent on the type of anions in the ionic liquids, in the order of $BF_4$>Cl>$PF_6$. The BMIBF 4-activated actuator showed the maximum displacement of 3.8 mm with low electrical power consumption at relatively low humidity. However, the BMICL-activated actuator showed a slight degradation of actuator performance. Further performance and durability improvement will be possible once various ionic liquids are blended with cellulose.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.96-100
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• 2004

Ion exchange polymer membrane in the dehydrated state was found to exhibit bending upon a small applied voltage, although the investigations on the hydrated ion exchange polymer membrane bending behavior have been performed quite intensively for more than a decade for the purpose of producing a practical polymer actuator. Our investigation on the dehydrated ion exchange polymer membrane has revealed that its bending direction is perfectly controllable by the polarity control of applied voltage and the degree of its bending curvature is also almost completely determined by the control of duration time of voltage application on it, while the hydrated ion exchange polymer membranes lack of such properties. Furthermore the longevity of dehydrated ion exchange polymer membrane sustaining such a highly controllable properties has been found quite longer than that of the hydrated ion exchange polymer membrane.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.4 s.247
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• pp.409-419
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• 2006

The actuating performance of plate-type unimorph piezoelectric composite actuators having various stacking sequences was evaluated by three dimensional finite element analysis on the basis of thermal analogy model. Thermal residual stress distribution at each layer in an asymmetrically laminated plate with PZT ceramic layer and thermally induced dome height were predicted using classical laminated plate theory. Thermal analogy model was applied to a bimorph cantilever beam and LIPCA-C2 actuator in order to confirm its validity. Finite element analysis considering thermal residual deformation showed that the bending behavior of piezoelectric composite actuator subjected to electric loads was significantly different according to the stacking sequence, thickness of constituent PZT ceramic and boundary conditions. In particular, the increase of thickness of PZT ceramic led to the increase of the bending stiffness of piezoelectric composite actuator but it did not always lead to the decrease of actuation distance according to the stacking sequences of piezoelectric composite actuator. Therefore, it is noted that the actuating performance of unimorph piezoelectric composite actuator is rather affected by bending stiffness than actuation distance.

• Macromolecular Research
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• v.14 no.6
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• pp.624-629
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• 2006

The cellulose-based, Electroactive Paper (EAPap) has recently been reported as a smart material with the advantages of lightweight, dry condition, biodegradability, sustainability, large displacement output and low actuation voltage. However, it requires high humidity.. This paper introduces an EAPap made with a cellulose solution and lithium chloride (LiCl), which can be actuated in room humidity condition. The fabrication process, performance test and effect of LiCl content of the EAPap actuator are illustrated. The bending displacement of the EAPap actuators was evaluated with actuation voltage, frequency, humidity and LiCl content changes. At a LiCl/ cellulose content of 3:10, the displacement output was maximized at a room humidity condition. Even though the displacement output was less than that of a high humidity EAPap actuator, the mechanical power output was not reduced due to the increased resonance frequency, which is promising for developing EAPap actuators that are less sensitive to humidity.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.203-204
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• 2008

Bacterial Cellulose Actuator with biocompatible and biodegradable properties was newly developed as an electro-active biopolymer under water. The performance of the BC actuator was improved through Li treatment. The mechanical and chemical properties of BC membranes were measured such as the tensile test, proton conductivity. The surface morphology of the bacterial cellulose was observed by using SEM. The electromechanical bending responses under both direct current and alternating current excitations were investigated. In voltage-current test,the power consumption under dynamic excitation increases with increasing voltage. Present results show that the bacterial cellulose actuator can be a promising smart material and may possibly have diverse applications under water.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.282-284
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• 2011

Based on graphene oxide and multi-walled carbon nanotube layers, a wireless bi-layer actuator that can be remotely controlled with an electromagnetic induction system has been developed. The graphene-based bi-layer actuator exhibits a large one-way bending deformation under eddy current stimuli due to asymmetrical responses originating from the temperature difference of the two different carbon layers. In order to validate one-way bending actuation, the coefficients of thermal expansion of carbon nanotube and graphene oxide are mathematically formulated in this study based on the atomic bonding energy related to the bonding length. The newly designed graphene-based bi-layer actuator is highly sensitive to electromagnetic wave irradiation thus it can trigger a new actuation mode for the realization of remotely controllable actuators and is expected to have potential applications in various wireless systems.

• Proceedings of the KIEE Conference
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• 1997.11a
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• pp.615-617
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• 1997

This paper reports experimental results on the fabrication and analysis of millimeter-sized bending actuators for active catheter by use of the shape memory alloy spring and the flexible beam. The major components of micro actuator are shape memory alloy spring, stainless steel strip and two acryl links. The micro actuator with the diameter of 2.0 mm and the length of 25 mm has been fabricated and characterized for the possible application to the micro active catheters. The measured maximum angle is $60^{\circ}$ and the response time is 5 sec.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.3
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• pp.537-543
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• 2002

This paper examines a new in-process measurement system for the measurement of micro-defects on the surfaces of brittle materials by using the AFM (Atomic Force Microscopy). A new AFM scanning stage that can also perform nano-scale bending of the sample was developed by adding a bending unit to a commercially available AFM scanner. The bending unit consists of a PZT actuator and sample holder, and can perform static and cyclic three-point bending. The true bending displacement of the bending unit is approximately 1.8mm when 80 volts are applied to the PZT actuator. The frequency response of the bending unit and the stress on the sample were also analyzed, both theoretically and experimentally. Potential surface defects of the sample were successfully detected by this measurement system. It was confirmed that the number of micro-defects on a scratched surface increases when the surface is subjected to a cyclic bending load.