• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.3
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• pp.337-342
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• 2011

Medical lift column controlling the vertical position while supporting heavy eccentric load should have the high fatigue strength as well as the extremely low structural deflection and vibration in order to maintain the positioning accuracy. The lift column driven by a induction motor is generally in a three-step sliding boom structure and exhibits the time-varying stress distribution according to the up-and-down motion. This study is concerned with the numerical prediction of the fatigue strength of the lift column subject to the time-varying stress caused by the up-and-down motion. The stress variation during a motion cycle is obtained by finite element analysis and the fatigue life is predicted making use of Palmgren-miner's rule and S-N curves. In order to secure the numerical analysis reliability, a 3-D FEM, model in which the detailed lift column structure and the fitting parts are fully considered, is generated and the interfaces between lift column and pads are treated by the contact condition.

• Transactions of the KSME C: Technology and Education
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• v.4 no.2
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• pp.93-99
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• 2016

High pressure nozzles and turbines of a gas turbine engine should be required to be operated under extreme operating conditions in order to maximize the performance. Engine manufactures have utilized nickel-base superalloys, enhanced cooling design, and thermal barrier coating techniques to overcome them and furthermore, material modeling, finite element analysis, optimization techniques, and etc. have been utilized widely for elaborate predictions. We aim to evaluate the effects on the low cycle fatigue life of the high pressure turbine blade caused by thermal barrier coatings and the cooling design of the endwall of the first stage turbine nozzle. To achieve it, the structural analysis, which utilized the results of conjugate heat transfer analysis as loading boundary conditions, was performed and then the results were the input for the assessment of low cycle fatigue life at several critical zones.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.2
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• pp.157-164
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• 2017

A parallel slide gate valve (PSGV) is located between the heat recovery steam generator (HRSG) and the steam turbine in a combined cycle power plant (CCPP). It is used to control the flow of steam and runs with repetitive operations such as startups, load changes, and shutdowns during its operation period. Therefore, it is necessary to evaluate the fatigue damage and the structural integrity under a large compressive thermal stress due to the temperature difference through the valve wall thickness during the startup operations. In this paper, the thermal-structural analysis and the fatigue life evaluation of a 16-inch PSGV, which is installed on the HP steam line, is performed according to the fatigue life assessment method described in the ASME B&PVC VIII-2; the method uses the equivalent stress from the elastic stress analysis.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.4
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• pp.234-243
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• 1992

Fatigue crack initiation life has a wide scatter and this makes the fatigue design of structural members difficult. In order to make the fatigue life distribution clear, it is required to prepare a large number of specimens and repeat the fatigue tests under the same loading condition. Such fatigue tests usually take much time and cost. In this study, a fatigue testing method using a multi-notched test specimen for the purpose of estimating the distribution function of fatigue crack initiation life by small number of fatigue tests is used. The purpose of this study is to verify the above fatigue testing method of a multi-notched specimen by using Bayesian reliability analysis, Least square method and Skewness method for the determination of unknown Weibull parameters. The multi-notched specimen is a specimen in which several tens of statistically identical notches are prepared.

• Journal of the Korea Convergence Society
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• v.11 no.1
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• pp.169-174
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• 2020

Side bolster is a part of the vehicle seat that holds the passenger's body from the side to make it more stable when the passenger is seated in the seat. In this study, the structural and fatigue analyses of the side bolsters at a car seat were carried out with two models of A and B. The heavily loaded parts, the damage by fatigue at driving a car and the difference of durability due to the structure were examined and the distributions of stress and deformation, and the fatigue lives were seen. Also, the strength and durability were examined. This study result is thought to be devoted to decrease the fatigue damage and increase the fatigue life and durability according to the design of bolster. This result is able to improve the product by applying the design of automotive side bolster practically. And it is thought to be the advantage to apply this study result to the convergence research with esthetic sense.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.3
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• pp.1085-1090
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• 2011

To assure the safety of rolling stock, it is important to perform the fatigue analysis of reduction gear unit in rolling stock considering a variation of velocity and traction motor capability. This paper presents fatigue analysis of the damage of reduction gear unit of railway vehicle under variable amplitude loading(VAL) based on quasi-static fatigue analysis using finite element model and linear Miner's rule. The VAL for the simulation was constructed from the tractive effort curve and train run curves of railway vehicle under commercial operation condition using MSC.ADAMS dynamic analysis. The finite element model for evaluating the carburizing effect on the gear surface was used for predicting the fatigue life of the middle gear based on strain-life based approach. The results showed that the frequent high starting torque due to a quick start as well as increasing numbers of stops at station would decrease the fatigue life of reduction gear unit.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2017.04a
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• pp.11-11
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• 2017

지속적인 고령화 추세에 따라 여성과 고령층의 노동력이 차지하는 비율이 높아지고 있어, 사용하기 편리한 소형농기계의 요구가 증가하고 있는 실정이다. 본 연구에서 사용한 소형 관리기는 정식 작업 전 경운, 정지 등 다양한 작업이 가능한 농기계이다. 본 연구에서는 소형 관리기에 토크 측정 시스템을 구성하였으며, 작업 중 가장 큰 부하를 받는 구굴 작업 부하를 측정하였다. 또한, 작업 시 가장 직접적으로 영향을 받는 PTO (Power Take Off) 기어의 부하 용량(load capacity)을 기어 해석 소프트웨어를 이용하여 분석하였다. PTO 기어의 부하 용량은 안전율, 피로수명을 대상으로 평가하였다. 측정된 부하 데이터는 변동 하중이므로, 부하 크기와 빈도수의 규칙적인 신호로 단순화하기 위하여 레인플로우 카운팅 방법을 사용하였으며, SWT (Smith-Watson-Topper) 방법을 이용하여 공칭 토크를 계산하였다. PTO 기어의 안전율은 ISO 6336, 피로 수명은 마이너 법칙(Miner rule)을 이용하여 계산하였다. PTO의 변속 단수 총 2단이며, 5개의 스퍼 기어로 구성되어 있다. 시뮬레이션 결과, 소형 관리기의 주행 속도 또는 PTO의 회전속도 증가에 따라 PTO에서 발생하는 평균 부하가 크게 나타났다. 또한 주행 단수 및 PTO 기어 단수가 증가할수록 기어의 안전율과 피로 수명이 감소하였으며, 특히 PTO 기어의 안전율은 접촉 응력에서의 안전율보다 굽힘 응력에서의 안전율이 급격하게 감소하였다. 소형 관리기의 PTO 수명은 주행 단수 2단, PTO 단수 2단 일 때 가장 적게 나타났다. 따라서 소형 관리기의 주행 속도와 PTO 회전 속도를 저속으로 작업하는 것이 PTO 기어의 수명에 더 유리할 것으로 판단된다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.1
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• pp.373-379
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• 2020

This study performed stress and fatigue life analysis of the damping hinge of a built-in side-by-side refrigerator that occurs when the door is opened to the maximum angle. An analysis of the initial design showed that stress concentration occurred at the corner between the cylinder and upper disk of the bracket pin, and the maximum stress exceeded the yield strength. The maximum stress location and the calculated fatigue life were consistent with the door opening-and-closing endurance test results for a prototype. Three cases of design improvement for the bracket pin were derived with the aim of reducing the stress concentration that appeared in the initial design. An analysis of the cases showed that inserting a fillet between the disk and the cylinder of the bracket pin reduced the stress and increased the fatigue life. Moreover, changing the disk into two steps was more favorable. In conclusion, the best design improvement was the case that the disk was changed to two steps and the fillet with a large radius was inserted. In that case, the stress was the smallest and the fatigue life was infinite.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.10
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• pp.1281-1289
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• 2011

This paper deals with several statistical distribution functions for the analysis of fatigue life data of composite laminates for small wind-turbine blades. A series of tensile tests was performed on triaxial glass/epoxy laminates for loading directions of $0^{\circ}$, $45^{\circ}$, and $90^{\circ}$. Then, fatigue tests were carried out to determine the fatigue life at the aforementioned loading directions and the fatigue stresses at four levels. Two-parameter Weibull, three-parameter Weibull, normal, and log-normal distributions were used to fit the fatigue life data of the triaxial composite laminates. The three-parameter Weibull distribution most accurately described the fatigue life data measured experimentally for all the cases considered. Furthermore, the variation of fatigue life was simultaneously affected by the loading direction and fatigue stress level.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.9
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• pp.596-603
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• 2020

'Electro-Mechanical Brake (EMB) is a novel braking system for automobiles and railway vehicles, and research in this area is actively underway. The current braking system for railway vehicles generates a braking force using a pneumatic cylinder, but the EMB system generates the force through a combination of an electric motor and gears. In this study, the design of an EMB system that meets the domestic standards was conducted through the finite element modeling and fatigue analysis of an eccentric rotating shaft-based EMB system capable of generating a high clamping force. At this time, to improve the accuracy of fatigue analysis, three types of fatigue test specimens, which were subjected to the same heat treatment as the materials used in the prototype, were produced, and the fatigue tests were performed for each material. The fatigue properties (S-N curves) were obtained from the fatigue test results for each material and reflected in the analysis model. The results of fatigue analysis confirmed that the design of the EMB prototype could satisfy the maximum commercial braking/relaxation of 530,000 times, which was the endurance life condition for domestic railway vehicles. In addition, based on this design, a prototype will be manufactured, and endurance testing will be completed to demonstrate the durability characteristics of the developed prototype.