• Smart Structures and Systems
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• v.1 no.3
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• pp.283-308
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• 2005

This paper features about the modeling and design of a fast output sampling feedback controller for a smart Timoshenko beam system for a SISO case by considering the first 3 vibratory modes. The beam structure is modeled in state space form using FEM technique and the Timoshenko beam theory by dividing the beam into 4 finite elements and placing the piezoelectric sensor/actuator at one location as a collocated pair, i.e., as surface mounted sensor/actuator, say, at FE position 2. State space models are developed for various aspect ratios by considering the shear effects and the axial displacements. The effects of changing the aspect ratio on the master structure is observed and the performance of the designed FOS controller on the beam system is evaluated for vibration control.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.06a
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• pp.37-40
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• 1998

In this paper, Pb(Z $r_{0.53}$ $Ti_{0.47}$) $O_3$+x[wt%]C $r_2$ $O_3$ ceramics were fabricated, and thermal aging effects on the specimen were investigated. After thermal aging, the temperature coefficients of their resonant frequence became stable and only the specimen with C $r_2$ $O_3$ additives in them could have lower temperature coefficientient

• Transactions of Materials Processing
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• v.25 no.6
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• pp.373-378
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• 2016

Recent researches have reported that the superposition of ultrasonic vibrations in metal forming provides beneficial effects such as the reduction of forming load, flow stress and interfacial friction which improves the surface quality of end products. This paper presents experimental investigations on the effects of ultrasonic vibrations in upsetting tests of aluminum. The ultrasonic exciting system consists of piezoelectric transducer and resonator was designed and constructed to superimpose high frequency oscillation on the forming tools. Ultrasonic vibration-assisted upsetting tests were performed for three vibration modes five amplitudes, and the results were compared with those of conventional upsetting tests. The results showed that the superimposition of ultrasonic vibration reduces the upsetting load, and the load reduction is only dependent on the amplitude of the applied vibration regardless of deformation histories and vibration modes.

• Structural Engineering and Mechanics
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• v.67 no.2
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• pp.143-153
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• 2018

Thermal buckling of nonlocal flexoelectric nanoplates incorporating surface effects is analyzed for the first time. Coupling of strain gradients and electrical polarizations is introduced by flexoelectricity. It is assumed that flexoelectric nanoplate is subjected to uniform and linear temperature distributions. Long range interaction between atoms of nanoplate is modeled via nonlocal elasticity theory. The residual surface stresses which are usually neglected in modeling of flexoelectric nanoplates are incorporated into nonlocal elasticity to provide better understanding of the physic of problem. A Galerkin-based approach is implemented to solve the governing equations derived from Hamilton's principle are solved. The verification of obtained results is performed by comparing buckling loads of flexoelectric nanoplate with previous data. It is shown that buckling loads of flexoelectric nanoplate are significantly affected by thermal loading type, temperature change, nonlocal parameter, surface effect, plate thickness and boundary conditions.

• Steel and Composite Structures
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• v.46 no.4
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• pp.513-523
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• 2023

Buckling and post-buckling behaviors of geometrically perfect double-curvature shells made from smart composites have been investigated. The shell has been supposed to be exposed to transverse mechanical loading and magneto-electro-elastic (MEE) coupling. The composite shell has been made of two constituents which are piezoelectric and magnetic ingredients. Thus, the elastic properties might be variable based upon the percentages of the constituents. Incorporating small scale impacts in regard to nonlocal theory leads to the establishment of the governing equations for the double-curvature nanoshell. Such nanoshell stability will be shown to be affected by composite ingredients. More focus has been paid to the effects of small scale factor, electric voltage and magnetic intensity on stability curves of the nanoshell.

• Journal of the Korean Ceramic Society
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• v.41 no.9
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• pp.709-714
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• 2004

The additive of low temperature sintering in Mn-doped PMN-PZT known as high piezoelectric materials was studied in this experiment. B$_2$O$_3$ was used for the additive of low temperature sintering. The effects of sintering temperature in dielectric, and piezoelectric properties were investigated with the amounts of B$_2$O$_3$. Sintered density was increased in comparison with no addition and under 2wt％ B$_2$O$_3$ and lower sintering temperature than 100$0^{\circ}C$. Therefore, in the low sintering temperature, the densification was improved by the addition of the B$_2$O$_3$. However, the sintering density was lower than that of the main composition in the case of the sintered at over 10$50^{\circ}C$. Dielectric constant with the addition of B$_2$O$_3$ was evaluated. The dielectric constant was 1000 2 wt％ of B$_2$O$_3$ and sintered at 100$0^{\circ}C$. Under 2wt％ of B$_2$O$_3$, the electromechanical coupling factor and the piezoelectric constant were not so much decreased. The electromechanical coupling factor and the piezoelectric constant were 50％ and 300(${\times}$10$^{-12}$ C/N) respectively. The mechanical quality factor was increased with B$_2$O$_3$. The mechanical quality factor was 1700 at 0.5wt％ B$_2$O$_3$ and sintered at 110$0^{\circ}C$. Dielectric loss was less than 0.5％ regardless of the amount of B$_2$O$_3$.

• Journal of the Korean Ceramic Society
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• v.19 no.4
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• pp.293-299
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• 1982

The effects of $MnO_2$ and $Cr_2O_3$ on the Piezoelectrictric properties of Pb(Mg1/2W1/2)0.3 Ti0.4 Zr0.3O3 Ceramics. Electromechanical properties in the system in connection with the sintering temperature and the effects of $MnO_2$ and $Cr_2O_3$ addition. The dielectric constant of the ceramics decreased with the additions of $MnO_2$ while the additions of $Cr_2O_3$ increased the value. The Planar coupling factor (Kp) of the ceramics with 0.2wt% $MnO_2$ and with 0.2wt% $Cr_2O_3$ gave the highest value of 0.52 and 0.513 as sintered at 106$0^{\circ}C$, 108$0^{\circ}C$, respectively. The value of mechanical Q-factor were in parallel with the fired density of the ceramics. The optical micrography of the sintered bodies showed that the additions of $MnO_2$ promoted the grain growth, while the additions of $Cr_2O_3$ retarded the grain growth.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.11
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• pp.1486-1496
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• 2000

The initial flame kernel development and flame propagation in a constant volume combustion chamber is analyzed by the heat release rate and the mass fraction burnt. The combustion pressure is measured with a piezoelectric type pressure sensor. In order to evaluate the effects of ignition system and ignition energy on the flame propagation, four different ignition systems are designed and tested, and the ignition energy is varied by the dwell time. Several different spark plugs are also tested and examined to analysis the effects of electrodes on flame kernel development. The results show that the when the dwell time is increased, and when the spark plug gap is extended, heat release rate and the mass burnt fraction are increased. The materials and shapes of electrodes affect the flame development, because they change the energy transfer efficiency from electrical energy to chemical energy. The diameter of electrodes influences not only the heat release rate but also the mass burnt fraction as well.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1487-1488
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• 2011

Electrical properties and microstructure were investigated on the effects of $MnO_2$ and the lead-free $(Na_{0.44}K_{0.52}Li_{0.04})(Nb_{0.83}Sb_{0.07}Ta_{0.1})O_3$ ceramics with the addition of $MnO_2$ were fabricated by a conventional mixed oxide method. A gradual change in the crystal and microstructure was observed with the increase of $MnO_2$ addition. For the NKN-LST-xmol%$MnO_2$ sintered at $1100^{\circ}C$, bulk density increased with the addition of $MnO_2$ and showed maximum value at addition 1.0mol% of $MnO_2$. Curie temperature of the NKN-LST ceramics slightly decreased with adding $MnO_2$. The dielectric constant, piezoelectric constant ($d_{33}$) and electromechanical coupling factor ($k_p$) increased below 0.25mol% of $MnO_2$ addition, which might be due to the increase in density. The high piezoelectric properties = 145 pC/N, electromechanical coupling factor = 0.421 and dielectric constant = 2883 were obtained for the NKN-LST-0.25mol%$MnO_2$ sintered at $1100^{\circ}C$ for 4h.

• Smart Structures and Systems
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• v.14 no.3
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• pp.327-345
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• 2014

This paper presents a composite control strategy for the active suppression of vibration due to the unknown disturbances, such as external excitation, harmonic effects and control spillover, as well as high-frequency accelerometer measurement noise in the all-clamped stiffened plate. The proposed composite control action based on the modal approach, consists of two contributions including feedback part and feedforward part. The feedback part is the well-known PID controller, which is widely used to increase the structure damping and improve its dynamic performance close to the resonance frequencies. In order to get better performance for vibration suppression, the weight matrixes is optimized by chaos sequence. Then an improved disturbance observer (IDOB) as the feedforward compensation part is developed to enhance the vibration suppression performance of PID under various disturbances and uncertainties. The proposed IDOB can simultaneously estimate the various disturbances dynamically as well as measurement noise acting on the system and suppress them by feedforward compensation design. A rigorous analysis is also given to show why the IDOB can effectively suppress the unknown disturbances and measurement noise. In order to verify the proposed composite control algorithm (IDOB-PID), the dSPACE real-time simulation platform is used and an experimental platform for the all-clamped stiffened plate active vibration control system is set up. The experimental results demonstrate the effectiveness, practicality and strong anti-disturbances ability of the proposed control strategy.