• 대한기계학회논문집A
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• 제31권1호
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• pp.70-76
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• 2007

Elastic-plastic fracture mechanics is popularly used for integrity evaluation of major components, however, it is not easy to extract standard specimens from operating facility. This paper examines how ductile fracture toughness is characterized by a small punch testing technique in conjunction with finite element analyses incorporating a damage model. At first, micro-mechanical parameters constituting Rousselier model are calibrated for typical nuclear materials using both estimated and experimental load-displacement (P-$\delta$) curves of miniaturized specimens. Then, fracture resistance (J-R) curves of relatively larger standard CT specimens are predicted by finite element analyses employing the calibrated parameters and compared with corresponding experimental ones. It was proven that estimated results by the proposed method using small punch specimen is promising and might be used as a useful tool for ductile crack growth evaluation.

• 전자공학회논문지SC
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• 제45권1호
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• pp.31-40
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• 2008

본 논문에서는 자기변형재료를 이용한 미세 구동기의 개발과 실시간 제어 알고리즘에 관한 내용을 다룬다. 자기변형재료는 빠른 응답속도, 미세변위동작, 높은 에너지 효율 등의 장점을 가지고 있어 미세 구동기의 재료로 적합하지만 히스테리시스 특성도 함께 갖고 있어 제어에 많은 어려움이 따른다. 본 논문에서는 자기변형재료의 히스테리시스를 제어하기위해 Preisach model을 바탕으로 구동기를 모델링 하였다. 기존의 Preisach 모델은 실험적 데이터를 바탕으로 하기 때문에 정밀한 제어를 하기 위해서는 많은 양의 데이터가 필요하고 결과적으로는 처리해야할 데이터의 양이 많아져 연산하는데 많은 시간이 걸리는 문제가 있다. 본 논문에서는 이러한 문제를 해결하기 위하여 기존의 Preisach 모델의 데이터를 선행 처리하여 일정구간 구동기의 움직임을 저장해 놓은 확장된 Preisach 모델을 제안하였다. 본 논문에서는 Tefenol-D라는 자기변형재료를 사용하여 미세구동기를 제작하고 제어 실험을 통하여 제안된 모델의 우수성을 증명하였다.

• 대한기계학회논문집
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• 제16권8호
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• pp.1493-1502
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• 1992

본 연구에서는 크랙선단의 소성변형에 의해 발생하는 소성유기 크랙개구거동 을 검토하기 위하여, 크랙선단 최인접 영역에서 COD를 측정할 수 있는 직접 측정법을 개발 사용하고 (1) 직접측정법의 적용범위와 크랙선단의 개구거동 (2) 측정위치에 따 른 개구하중의 변화 (3) 개구비에 영향을 주는 하중변수등에 대하여 고찰하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.35-39
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• 2008

In this study, electromechanical properties of carbon nanotube (CNT) thin film on flexible substrates were measured using a micro-tensile machine with functionality of simultaneous measurements of displacement, load and electrical resistance. The CNT thin film of about 100 nm thick was deposited on flexible substrates, polyethylene terephthalate (PET) using spraying and ink-jetting techniques. To investigate the effect of process condition on the electromechanical properties of CNT thin film, sets of CNT samples were fabricated under various heat treatments and microwave process. The microstructures of the CNT thin film before and after tensile test were investigated using Scanning Electron Microscope (SEM), and the failure modes of the CNT thin films were identified to understand their electromechanical behaviors and interaction with the flexible substrates. Based on the experimental results, the use of CNT thin film as flexible electrodes and strain gages is discussed.

• Smart Structures and Systems
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• 제19권5호
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• pp.553-565
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• 2017

Structural modeling of unencapsulated ionic polymer metal composite (u-IPMC) actuators that are used for flapping the insect scale-flapping wing of micro air vehicles (FMAV) in dry environmental conditions is carried out. Structural modeling for optimization of design parameters for retention of water, maximize actuation performance and to study the influence of water activity on the actuation characteristics of u-IPMC is explored for use in FMAV. The influence of equivalent weight of Nafion polymer, cations, concentration of cations, pre-treatment procedures on retention of water of u-IPMCs and on actuation parameters, flapping angle, flexural stiffness and actuation displacement are investigated. IPMC designed with Nafion having equivalent weight 900-1100, pre-heated at $30^{\circ}C$ and with sodium as the cations is promising for optimum retention of water and actuation performance. The actuation parameters while in operation in dry and humid environment with varying water activity can be tuned to desirable frequency, deflection, flap angle and flexural stiffness by changing the water activity and operational temperature of the environment.

• 한국정밀공학회지
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• 제27권10호
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• pp.84-92
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• 2010

In this study a numerical analysis has been conducted for the flow characteristics and pumping performance of a piezoelectric-based micropump with electromagnetic resistance exerted on electrically conducting fluid. Here, electromagnetic resistance is alternately applied at the inlet and outlet with alternately applied magnetic fields in association with the reciprocal membrane motion of the piezoelectric-based micropump. A model of Prescribed Deformation is used for the description of the membrane motion. The internal flow characteristics and pumping performance are investigated with the variation of magnetic flux density, tube size, displacement of membrane and the frequency of the membrane. It turns out that the current micropump has a wide range of pumping flow rate compared with diffuser-nozzle based micropumps.

• Journal of Mechanical Science and Technology
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• 제20권11호
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• pp.1914-1919
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• 2006

Recently, the microrobots powered by biological muscle actuators were proposed. Among the biological muscle actuators, frog muscle is well known as a good muscle actuator and has a large displacement, actuation forces and piezoelectric properties. Therefore, for the application of the biomimetic microrobot, this paper reports the electromechanical properties of frog muscle. First of all, the experimental setup has been established for measuring generative force of the frog muscle. Through the various electrical stimulating inputs to the frog muscle, we measured the contractile force of the frog muscle. From the measuring results, we found that the actuating contractile force responses of the frog muscle are determined by the amplitude, frequency, duty ratio, and wave form of the stimulation signal. This study will be beneficial for the development of the microrobot actuated by frog muscle.

• 정보저장시스템학회:학술대회논문집
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• 정보저장시스템학회 2005년도 추계학술대회 논문집
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• pp.190-194
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• 2005

There is a great demand of micro-actuators for mobile information devices such as SFF optical drives and mobile camera phones. However, conventional magnetic coils of electromagnetic motors are a major obstacle for miniaturization because of their complicated structures and large power consumption. In this paper, a linear ultrasonic motor to actuate focusing lens of mobile devices is proposed. The new actuator uses a ring type bimorph piezoelectric material, and $d_{31}$ mode is adopted for applying linear motion. The interaction between inertia force and friction force makes linear motion by high-frequency saw signal input. The saw signal gives steady forces on the one direction by asymmetric inclination property of the signal itself on time domain. A commercial FEM (ANSYS) was used in this investigation for simulating structural analysis, identification of dynamic property, such as resultant displacement and coupled analysis with piezoelectric material. To evaluate the performance of the new design, a prototype was manufactured and experiments were carried out. Experimental results show the actuator motion of 1.52 mm/s at 10 kHz input signal in 5 V.

• 정보저장시스템학회논문집
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• 제2권4호
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• pp.251-256
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• 2006

There is a great demand of micro-actuators for mobile information devices such as SFF optical drives and mobile phone cameras. However, the magnetic coils used in conventional electromagnetic motors are a major obstacle for the miniaturization because of their complicated structures and large power consumption. In this paper, a linear ultrasonic motor to actuate focusing lens of mobile devices is proposed. The new actuator uses a ring type bimorph piezoelectric material, and $d_{31}$ mode is adopted for applying linear motion. The interaction between inertia force and friction force makes linear motion by high-frequency saw signal input. The saw signal gives steady forces on the one direction by asymmetric inclination property of the signal itself on time domain. A commercial FEM(ANSYS) was used in this investigation for simulating structural analysis, identification of dynamic property, such as resultant displacement and coupled analysis with piezoelectric material. To evaluate the performance of the new design, a prototype was manufactured and experiments were carried out. Experimental results show the actuator motion of 5.4 mm/s at 10V saw signal of 41 kHz.

• 유공압시스템학회논문집
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• 제8권1호
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• pp.19-25
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• 2011

This study presents the design of digital amplifier.controller for a proportional control valve and the development of PID discrete control scheme by using RCP(Rapid Controller Prototyping) system. RCP system is the device to embed the control code developed in PC into the microcontroller on-site. Ramp input test using the digital amplifier.controller developed in this study was carried out for the proportional control valve of domestic production and Bosch Rexroth respectively. The instability problem occurred around maximum displacement of localized valve spool at ramp input test was solved by supplementing offset current to the duty ratio of PWM(Pulse Width Modulation) driving signal to the solenoid. The comparison of test results between localized proportional control valve and Bosch Rexroth's product shows that the characteristics obtained by ramp input test and static flow gains are alike each other. Two valves are about the same in dead bands and hysteresis characteristics.