• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.684-687
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• 2004

일반적으로 적층형 압전 액츄에이터의 변위는 액츄에이터의 내부 적층수와 압전정수($d_{33}$)에 비례적으로 증가한다. 그러나 압전현상을 이용한 액츄에이터는 전기적, 기계적 부하에 의한 dipole 거동을 보이기 때문에 domain wall에 의한 압전정수의 비선형 거동을 보인다. 본 논문에서는 PMN-PZ-PT 세라믹스를 이용하여 $2{\times}3{\times}10$ (mm)의 적층형 세라믹 액츄에이터를 제조 후 1kV/mm의 일정한 전계를 인가하고 $0\sim990N$의 기계적 부하 인가하에서 적층형 세라믹 액츄에이터의 비선형 특성을 조사하였다. 압전 액츄에이터의 비선형 거동은 기계적 응력에 의한 유전 및 전왜 특성에 영향주고, 액츄에이터의 변위 특성은 유전 및 전왜 특성의 영향에 크게 의존한다.

• The Journal of the Acoustical Society of Korea
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• v.14 no.5
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• pp.83-88
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• 1995

The common practice for the identification of piezoelectric properties is based on the use of immittance of a resonator with a certain geometry and poling direction. In this paper, a new method is suggested to identify the complex-valued piezoelectric material constants. This method Is based on the minimization of differences between the analytical immittance and the experimental measurement of resonator. Non-linear minimization problems are formulated to find out the unknown properties relevant to the resonators. The immittance data used for identification are measured at a number of frequencies which cover the vicinity of resonance frequency and the low frequency region. To illustrate the proposed technique, the complex-valued coefficients are identified for a typical PZT4 ceramic composition.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.3
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• pp.255-263
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• 2017

This paper presents a beam element capable of conducting material and geometric nonlinear analysis for applications requiring the ultimate behavioral analysis of structures with composite cross-sections. The element formulation is based on co-rotational kinematics to simulate geometrically nonlinear behaviors, and it uses the fiber section method to calculate the stiffness and internal forces of the element. The proposed element was implemented using an in-house numerical program in which an arc-length method was adopted to trace severe nonlinear responses(such as snap-through or snapback), as well as ductile behavior after the peak load. To verify the proposed method of element formulation and the accuracy of the program that was used to employ the element, several numerical studies were conducted and the results from these numerical models were compared with those of three-dimensional continuum models and previous studies, to demonstrate the accuracy and computational efficiency of the element. Additionally, by evaluating an example case of a frame structure with a composite member, the effects of differences between composite material properties such as the elastic modulus ratio and strength ratio were analyzed. It was found that increasing the elastic modulus of the external layer of a composite cross-section caused quasi-brittle behavior, while similar responses of the composite structure to those of homogeneous and linear materials were shown to increase the yield strength of the external layer.

• Journal of Korean Tunnelling and Underground Space Association
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• v.2 no.2
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• pp.72-85
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• 2000

Rock is a very complex and heterogeneous material, containing structural flaws due to geologic generation process. Because of those structural flaws, deformation and failure of rock when subjected to differential compressive stresses is non-linear. To simulate the non-linear behavior of rock, mechanical crack models, that is, sliding and shear crack models have been used in several studies. In those studies, non-linear stress-strain curves and various behaviors of rock including the changes of effective elastic moduli ($E_1$, $E_2$, ${\nu}_1$, ${\nu}_2$, $G_2$) due to crack growth were simulated (Kemeny, 1993; Jeon, 1996, 1998). Most of the studies have mainly focused on the verification of the mechanical crack model with relatively less attempt to apply it to practical purposes such as numerical analysis for underground and/or slope design. In this study, the validity of mechanical crack model was checked out by simulating the non-linear behavior of rock and consequently it was applied to a practical numerical analysis, finite element analysis commonly used.

• Electrical & Electronic Materials
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• v.8 no.1
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• pp.27-34
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• 1995

The analysis of nonlinear equivalent circuit and the resonance characteristics of input current and output voltage were simulated, and their electrical properties are discussed in the transverse-type piezoelectric ceramic transformer. The nonlinear resonance characteristics of input current and output voltage showed by the thermal effect due to a higher driving current, the nonlinearity increased greatly as driving current increased. When load resistor was 100[M.ohm.], the nonlinear coefficient was -1.3. The nonlinear resonance curve of input current and output voltage for a variation of input voltage and load resistor agreed with the discussed theory. The output voltage increased nearly proportioned to input voltage when load resistors were below 50[M.ohm.], the voltage step-up ratio decreased when a load resistor was 100[M.ohm.] and their maximum value was 950.

• Computational Structural Engineering
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• v.7 no.3
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• pp.115-122
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• 1994

Design sensitivity analysis of the second order perturbed eigenproblems for random structural system is presented. Dynamic response of random system including uncertainties for the design variable is calculated with the first order and second order perturbation method to original governing equation. In optimal design methods, there is fundamental requirement for design gradients. A method for calculating the sensitivity coefficients is developed using the direct differentiation method for the governing equation and first order and second order perturbed equation.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.5
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• pp.1563-1571
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• 1991

본 연구에서는 가상일 원리로 부터 유한 요소 수식화를 updated-Lagrangian 형태로 유도하였으며, 유도된 수식화를 연속체 유한 요소로 유한 근사화 하였다. 이 때 초소성 재료의 거동은 비압축성, 비선형 점성 유ㄷ옹으로 묘사하였다. 유한 요소 프로그램은 성형 기구 해석과 하중 압력을 제어하는 기법으로 구성되어 있으며 하중 압력의 제어는 성형 시간이 최소가 되게 하기 위하여 변형률 속도 민감 계수가 최대가 되고, 국부 변형에 의한 두께 감소를 방지하며 변형률 속도는 일정하게 유지되면서 성 형이 될 수 있도록 하였다. 즉 하중 압력 제어는 상당 변형률 속도가 최대가 되게하 여 성형 시간을 최소화하게 구성하였다.개발된 유한 요소 프로그램은 정수압 벌징 가공에 적용하였으며 최적 압력 시간 선도, 성형 형상, 두께 및 두께 변형률 분포, 상 당 변형률 분포 등을 구하였다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.5
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• pp.169-178
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• 2008

Compressive flanges of steel box girder is designed based on the ultimate strength behavior of sub-panel which is enclosed with longitudinal stiffeners and transverse stiffeners on appropriate safety factor. However, it is rational that the ultimate strength is calculated considering the various factors such as number and stiffness of longitudinal stiffener, spacing of transverse stiffener, initial deformation and residual stress distribution. In this study, an analysis program based on Folded Plate theory is developed considering the geometric effects and the material nonlinearity. The analysis program is applicated to the steel box girder bridges which is really constructed in domestic.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.04a
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• pp.298-305
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• 1996

The common practice for the identification of piezoelectric properties is based on the use of immittance behavior of a resonator with a certain geometry and poling direction. In this paper, a new method is suggested to identify the complex-valued piezoelectric material constants. This method is based on the minimization of differences between the analytical immittance and the experimental measurement of resonator. Non-linear minimization problems are formulated to find out the unknown properties relevant to the resonators. The immittance data used for identification are measured at a number of frequencies which cover the vicinity of resonance frequency and the low frequency region. To illustrate the proposed technique, the complex-valued coefficients are identified for a typical PZT4 ceramic composition.

• Journal of the Korean Society for Railway
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• v.13 no.1
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• pp.84-91
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• 2010

We built multi-purpose large triaxial testing system that can test and evaluate various geotechnical design parameters such as shear strength, deformation modulus and stress-strain behaviour for large diameter granular materials, which are the most commonly used construction materials in the railway, road embankments. The details of the built testing system and the results obtained from static triaxial test carried out for gneiss ballast material are discussed within the scope of this paper. Ballast is hardly saturated and is confined at low overburden pressure, since the depth is shallow and the permeability is very high. Herein we ascertained that the confining pressure can effectively be controlled by vacuum. The rational trend could be checked up through triaxial test results such as shear strength, deformation, and particle breakage. And the shear strength envelope could be non-linearly represented with the parent rock strength, confining pressure of the triaxial test and proper parameters.