• Tribology and Lubricants
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• 제37권2호
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• pp.48-53
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• 2021

Wind energy is considered as the most competitive energy source in terms of power generation cost and efficiency. The power train of the pitch drive for a wind turbine uses a 3-stage complex planetary gear system in being developed locally. A gear train of the pitch drive consists of an electric or hydraulic motor and a planetary decelerator, which optimizes the pitch angle of the blade for wind generators in response to the change in wind speed. However, it is prone to many problems, such as excessive repair costs in case of failure. Complex planetary gears are very important parts of a pitch drive system because of strength problem. When gears are designed for the power train of a pitch drive, it is necessary to analyze the fatigue strength of gears. While calculating the specifications of the complex planetary gears along with the bending and compressive stresses of the gears, it is necessary to analyze the fatigue strength of gears to obtain an optimal design of the complex planetary gears in terms of cost and reliability. In this study, the specifications of planetary gears are calculated using a self-developed gear design program. The actual gear bending and compressive stresses of the planetary gear system were analyzed using the Lewes and Hertz equation. Additionally, the calculated specifications of the complex planetary gears were verified by evaluating the results from the Stress - No. of cycles curves of gears.

• 마이크로전자및패키징학회지
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• 제24권1호
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• pp.103-111
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• 2017

본 연구에서는 전동차의 전력 변환 장치로 많이 사용되고 있는 고전압 대전류용(3,300 V/1200 A급) insulated gate bipolar transistor(IGBT) 모듈에 대하여 열 사이클 조건하에서의 열-기계적 응력해석 및 피로수명해석을 수행하였다. 특히 최근 고전압 IGBT용으로 개발되고 있는 구리(copper) 와이어, 리본(ribbon) 와이어를 사용하였을 경우의 응력 및 피로수명을 기존의 알루미늄 와이어와 비교하여 분석하였다. 알루미늄 와이어 보다는 구리 와이어에 응력이 3배 이상 많이 발생하였다. 리본 와이어의 경우 원형 와이어 보다 응력이 더 크게 발생하며, 구리 리본 와이어의 응력이 제일 높았다. 칩과 direct bond copper(DBC)를 접합하고 있는 칩 솔더부의 피로해석을 수행한 결과, 솔더의 크랙은 주로 솔더의 모서리에서 발생하였다. 원형 와이어를 사용할 경우 솔더의 크랙은 약 35,000 사이클에서 발생하기 시작하였으며, 알루미늄 와이어 보다는 구리 와이어에서의 크랙의 발생 면적이 더 컸다. 반면 리본 와이어를 사용하였을 경우 크랙의 면적은 원형 와이어를 사용하였을 경우보다 적음을 알 수 있다. DBC와 베이스 플레이트 사이에 존재하는 솔더의 경우 크랙의 성장 속도는 와이어의 재질이나 형태에 관계없이 비슷하였다. 그러나 칩 솔더에 비하여 크랙의 발생이 일찍 시작하며, 40,000 사이클이 되면 전체 솔더의 반 이상이 파괴됨을 알 수 있었다. 따라서 칩 솔더 보다는 DBC와 베이스 플레이트 사이에 존재하는 솔더의 신뢰성이 더 큰 문제가 될 것으로 판단된다.

• 대한기계학회논문집B
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• 제34권2호
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• pp.137-143
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• 2010

발전기 고정자 권선 내부의 완전 건조는 누수시험을 위한 필요/충분조건이다. 발전기 운전에 의한 고주기 피로는 미세 균열 발생의 원인이 되고, 미세 균열에서의 물분자는 누설 진단의 신뢰성을 저하시킨다. 이와같은 이유로, 발전기 고정자 권선에 대한 누수시험에서 권선에 누설처가 있음에도 불구하고 누설이 없다는 결론과 같은 오류를 범하고 있다. 발전기 제작사는 누수시험을 고유한 건조 판정 기준을 제시하고 있지만, 실제로는 어떤 판정 기준도 누수시험을 위해 정확하게 건조 판정 기준을 지시하고 있지는 못하고 있는 실정이다. 그 이유는 발전기 고정자 권선의 복잡한 구조와 효과적인 건조 장비의 부재 때문이다. 본 논문에서는 수 냉각 발전기 고정자 권선의 내부 건조 여부를 판정하기 위한 건조 판정 기준을 완벽하게 제안하였으며 실험적으로 증명하였다.

• Corrosion Science and Technology
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• 제6권3호
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• pp.103-111
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• 2007

The effect of stress factors on the growing process of stress corrosion cracking (SCC) of the sensitized 18-8 stainless steel in high temperature water was investigated using equations of crack growth rate derived from applying electric circuits to SCC corrosion paths. Three kinds of cross sections have to be considered when electric circuit is constructed using total current. The first is ion flow passage area, $S_{sol}$, of solution in crack, the second is total dissolving surface area, $S_{dis}$, of metal on electrode of crack tip and the third is dissolving cross section, $S_{met}$, of metal on grain boundary or in base metal or in welding metal. Stress may affect each area. $S_{sol}$ may depend on applied stress, $\sigma_{\infty}$, related with crack depth. $S_{dis}$ is expressed using a factor of $\varepsilon(K)$ and may depend on stress intensity factor, K only. SCC crack growth rate is ordinarily estimated using a variable of K only as stress factor. However it may be expected that SCC crack growth rate depends on both applied stress $\sigma_{\infty}$ and K or both crack depth and K from this consideration.$\varepsilon(K)$ is expressed as ${\varepsilon}(K)=h_2{\cdot}K^2+h_3{\cdot}K^3$ when $h_{2}$ and $h_{3}$ are coefficients. Also, relationships between SCC crack growth rate, da/dt and K were simulated and compared with the literature data of JBWR-VIP-04, NRC NUREG-0313 Rev.2 and SKIFS Draft. It was pointed out in CT test that the difference of distance between a point of application of force and the end of starter notch (starting point of fatigue crack) may be important to estimate SCC crack growth rate. An anode dissolution current density was quantitatively evaluated using a derived equation.

• Journal of Welding and Joining
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• 제30권6호
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• pp.74-79
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• 2012

It depends on the joint configuration, dimensions and constraints of the joint whether the residual stress at the root of single-sided butt weld is tensile or not. Therefore, recommendation is generally made that high R ratio should be used in the fatigue test of welded joint in order to prevent excessively long life caused by compressive residual stress. In this research, the residual stress profile in butt weld joint was obtained through compliance method, using successive extension of a slot and measurement of the variation of strain during the slot extension. The residual stress profile was firstly assumed to be the linear summation of Legendre polynomials up to 9th order excluding 0th and 1st order. Strain variation on the surface was measured while the slot was being extended by cutting to find out the 8 unknown coefficients of each polynomial term. The cut was made by the electric discharge machine. It was concluded that the residual stress near the surface is positive valued, however, it turned into the negative value as soon as it passed through 2 or 3 mm of the depth.

• 한국해양공학회지
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• 제1권1호
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• pp.127-137
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• 1987

The evaluation of the elastic-plastic fracture toughness $J_{1C}$ was performed on the center of weld metal(CWM), the heat affected zone (HAZ) and the base metal (BM) of API 5LB steel pipes welded by the high frequency electric resistance welding. The $J_{1C}$ was evaluated by the JSME R-Curve and JSME SZW methods using the smooth and side-grooved specimens. The results are as follows; (1) The $J_{1C}$ values by the SZW method are overestimated as compared with those by the R-curve method, because the micro-crack is formed as SZW increase with the deformation at SZ after initiation of the ductile crack. (2) The everage of $J_{1C}$ values by the the R-curve and the SZW methods in side-grooved specimens tended to decrease in comparison with smooth specimens 9.42% at CWM, 4.2% at HAZ, 23.2% at BM, respectively. (3) The boundary of the fatigue pre-crack, stretched zone, and dimple regions appeared more clearly in side-grooved specimens, for the slight change of SZW in the direction of the plate thickness, as compared with smooth specimens.

• 한국산업융합학회 논문집
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• 제3권2호
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• pp.131-139
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• 2000

Gear train in the automobile to be used for controlling gas flow in automobiles consists of spur gears with involute tooth type in multiple stages. This spur gear is designed considering to the high power transfer efficiency, bending stress and contact stress in the static and dynamic analysis. The torque has been increased simultaneously the angular velocity has been decreased through the stages after being supplied by AC synchronous motor. This apparatus is controlled by electrical devices such as the PIC microprocessor, hall sensor and other electric components. By comparing the preset data of PIC microcomputer which is supplied by external DC electric power with the value set of hall sensor which detects the rotation angle position, PIC microcomputer thus controls AC motor and gear train according to the program algorithm which includes the on-off control and PWM motor driving method. As the result of the experiment such as performance, fatigue, torque test, we can conclude that this system is superior to the same and familiar foreign systems.

• 전기학회논문지P
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• 제63권1호
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• pp.46-49
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• 2014

$Pb(Zr_{0.52}Ti_{0.48})O_3(PZT)$ thin films deposited on $Ru/RuO_2$ bottom electrode that grown for in-situ progress used rf magnetron sputtering method. We investigated the dependence of the crystalline and electrical properties in the way of capacitors PZT thin films. Our results show that all PZT films indicated polycrystalline perovskite structure with preferred orientation (110) and no pyrochlore phase is observed. The electric properties of the Ru improved with increasing Ru thin films thickness. A well-fabricated Ru/PZT/Ru (100 nm) /$RuO_2$ capacitor showed a leakage current density in the order of $2.03{\times}10^{-7}$ $A/cm^2$ as a 50 kV/cm, a remnant polarization (Pr) of 9.22 ${\mu}C/cm^2$, and a coercive field (-EC) of -32.22 kV/cm. The results show that $Ru/Ru/RuO_2$ bottom electrodes are expected to reduce the degradation ferroelectric fatigue and excellent ferroelectric properties.

• Journal of Electrical Engineering and Technology
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• 제10권3호
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• pp.952-957
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• 2015

Recently, the interior permanent magnet (IPM) motors for electric vehicle (EV) traction motor are being extensively researched because of its high energy density and high efficiency. The traction motor for EV requires high power and high efficiency at the wide driving region. Therefore, it is essential to fully consider the characteristics of the motor from low speed to high-speed driving regions. Especially, when the motor is driven at high speed, a significant centrifugal force is applied to the rotor. Thus, the rotor must be stably structured and be fully endured at the critical speed. In this paper, aims to examine the characteristics of the IPM motor by adjusting the width of air-barrier according to the permanent magnet position which is critical in designing an IPM motor for EV traction motors and to conduct a centrifugal force analysis for grasping mechanical safety.

• 한국전기전자재료학회논문지
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• 제14권9호
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• pp.731-735
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• 2001

S $r_{0.89}$B $i_{2.4}$T $a_2$ $O_{9}$ (SBT) thin films are deposited on Pt-coated electrode(Pt/Ti $O_2$/ $SiO_2$/Si) using RF magnetron sputtering method. In the XRD pattern, the SBT thin films had (105) orientation. As annealing temperature was increased from $600^{\circ}C$ to 85$0^{\circ}C$, the intensities of peak were increased. In the SEM images, Bi-layered perovskite phase was crystallized above $650^{\circ}C$ and rod-like grains grew above 75$0^{\circ}C$. The maximum remanent polarization and the coercive electric field at annealing temperature of 75$0^{\circ}C$ are 11.60$\mu$C/$\textrm{cm}^2$ and 48kV/cm respectively. The dielectric constant and leakage current density at annealing temperature of 75$0^{\circ}C$ are 213 and 1.01x10$^{-8}$ A/$\textrm{cm}^2$, respectively. The fatigue characteristics of SBT thin filmsdid not change up to 10$^{10}$ switching cycles.s.s.