• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.15 no.2
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• pp.19-30
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• 2019

In this study, to evaluate conservatism of various fatigue life evaluation procedures, fatigue tests were conducted using compact tension (CT) specimens with a round notch, made of A516 Gr.70 carbon steel and A240 TP304 stainless steel, under load-controlled cyclic condition. Experimental fatigue failure cycles were measured and compared with predicted fatigue lives using two different life evaluation methods; (1) Design-By-Analysis (DBA) procedure given in ASME B&PV Code, Sec. III, Div. 1, Subsec. NB-3200 and (2) structural stress-based approach provided in ASME B&PV Code, Sec. VIII, Div. 2, Part 5. To predict fatigue failure cycles, three-dimensional elastic finite element analysis was conducted. Fatigue lives were predicted by both design fatigue curve given in ASME B&PV Code, Sec. III, Div. 1, Appendices and best-fit fatigue curve suggested in NUREG/CR-6815 for the DBA procedure. Finally, fatigue lives evaluated by various methods were compared with test results, and then conservatism between each evaluation procedure was discussed.

• Journal of the Korean Society for Railway
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• v.8 no.2
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• pp.170-175
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• 2005

This study presents a prediction of a failure rate in a safety required system that consists of a embedded control system, requiring a satisfaction of a quantitative safety requirement. International Standards are employed to achieve a regular procedures in the whole life cycle of a system, for the purpose of a prediction and a evaluation of a fault that might be able to be happened in a system. This International Standards uses SIL (Safety Integrity Level) to evaluate a safety level of a system. SIL is divided into 4 levels, from level 1 to level 4, and each level has functional failure rate and dangerous failure rate of a system. In this paper we describe the conventional method to predict the dangerous failure rate and propose a method using hazard analysis to predict the dangerous failure rate. The conventional method and the technique using hazard analysis to predict the dangerous failure rate are made a comparison through the control modules of the interlocking system in KTX. The proposed method verify better effectiveness for the prediction of the dangerous failure rate than that of the conventional method.

• Journal of Korean Institute of Industrial Engineers
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• v.36 no.1
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• pp.69-77
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• 2010

The failure rate model of External Environment Maintenance(EEM) for a system under severe environment is investigated. EEM, which is recently introduced concept, is a maintenance activity controlling external environment factors that potentially cause system failure such as cleaning equipment, controlling temperature (humidity) and removing dust inside of electronic appliances. EEM can not have any influence on the inherent failure rate of a system but reduce the severity of the external environment causing failure since it deals with only external environment factors. Therefore, we propose two failure rate models to express the improvement effect of EEM: The intensity reduction model and age reduction model. The intensity and age reduction models of EEM are developed assuming the quality of improvement effect is proportioned to an extra intensity or age respectively. The validation of proposed failure rate models is performed in order of data generation, parameter estimation and test for goodness-of-fit.

• Journal of Applied Reliability
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• v.16 no.1
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• pp.56-63
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• 2016

Purpose: The purpose of this study is to point out that the Kaplan-Meier method is not valid to calculate the survival probability or failure probability (risk) in the presence of competing risks and to introduce more valid method of cumulative incidence function. Methods: Survival analysis methods have been widely used in biostatistics division. However the same methods have not been utilized in reliability division. Especially competing risks cases, where several causes of failure occur and the occurrence of one event precludes the occurrence of the other events, are scattered in reliability field. But they are not noticed in the realm of reliability expertism or they are analysed in the wrong way. Specifically Kaplan-Meier method which assumes that the censoring times and failure times are independent is used to calculate the probability of failure in the presence of competing risks, thereby overestimating the real probability of failure. Hence, cumulative incidence function is introduced and sample competing risks data are analysed using cumulative incidence function and some graphs. Finally comparison of cumulative incidence functions and regression type analysis are mentioned briefly. Results: Cumulative incidence function is used to calculate the survival probability or failure probability (risk) in the presence of competing risks and some useful graphs depicting the failure trend over the lifetime are introduced. Conclusion: This paper shows that Kaplan-Meier method is not appropriate for the evaluation of survival or failure over the course of lifetime. In stead, cumulative incidence function is shown to be useful. Some graphs using the cumulative incidence functions are also shown to be informative.

• Smart Structures and Systems
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• v.33 no.3
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• pp.177-188
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• 2024

The fatigue-induced sequential failure of a structure having structural redundancy requires system-level analysis to account for stress redistribution. System reliability-based design optimization (SRBDO) for preventing fatigue-initiated structural failure is numerically costly owing to the inclusion of probabilistic constraints. This study incorporates the Branch-and-Bound method employing system reliability Bounds (termed the B³ method), a failure-path structural system reliability analysis approach, with a metaheuristic optimization algorithm, namely grey wolf optimization (GWO), to obtain the optimal design of structures under fatigue-induced system failure. To further improve the efficiency of this new optimization framework, an additional bounding rule is proposed in the context of SRBDO against fatigue using the B³ method. To demonstrate the proposed method, it is applied to complex problems, a multilayer Daniels system and a three-dimensional tripod jacket structure. The system failure probability of the optimal design is confirmed to be below the target threshold and verified using Monte Carlo simulation. At earlier stages of the optimization, a smaller number of limit-state function evaluation is required, which increases the efficiency. In addition, the proposed method can allocate limited materials throughout the structure optimally so that the optimally-designed structure has a relatively large number of failure paths with similar failure probability.

• Journal of Korea Technology Innovation Society
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• v.16 no.1
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• pp.346-366
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• 2013

The importance of challenging and creative research recently has been increased, risk-taking on the R&D is being needed. The settlement of policy is urgently required in order to protect the result of high-risk research. 'Honorable Failure' is statutory by 'Regulation on the National R&D Program management' to resolve this issue, however its standards and detailed guides are not provided enough or the ministerial funding agencies apply different guidelines, making the researchers on the field confused by far. Therefore this paper reviews the current state of 'Honorable Failure Policy'(saving the 'failed' research despite of its adequate process or performance) and compares with the cases of major countries, then points out following issues; the uncertainty of the criterion, the difference of the main agent performing evaluation, admission of the failure, the utilization of the result of 'failed' research, the vagueness of the range of sanctions and restriction, and the lack of method of inspection and prevention for repetitive failure of the research projects. Finally, this paper proposes the solutions for these issues to improve.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.2 s.48
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• pp.1-10
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• 2006

Reinforced concrete bridge columns with relatively small aspect ratio show flexure-shear behavior, which is flexural behavior at initial and medium displacement stages and shear failure at final stage. Since the columns with flexure-shear failure have lower ductility than those with flexural failure, shear capacity curve models shall be applied as well as flexural capacity curve in order to determine ultimate displacement for seismic design or performance evaluation. In this paper, a modified shear capacity curve model is proposed and compared with the other models such as the CALTRANS model, Aschheim et al.'s model, and Priestley et al.'s model. Four shear capacity curve models are applied to the 4 full scale circular bridge column test results and the accuracy of each model is discussed. It may not be fully adequate to drive a final decision from the application to the limited number of test results, however the proposed model provides the better prediction of failure mode and ultimate displacement than the other models for the selected column test results.

• Journal of the Korea Concrete Institute
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• v.16 no.1 s.79
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• pp.10-17
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• 2004

Shear tests were performed on four ends of full scale U-type beams which were designed by optimum process for the depth with a live load of 4903Pa. The ratio of width to depth of full scale 10.5 m-span, composite U-type beams with topping concrete was greater than 2. Following conclusions were obtained from the evaluation on the shear performance of these precast prestressed beams. 1) Those composite U-type beams performed homogeneously up to the failure load, and conformed to ACI Strength design methods in shear and flexural behaviors. 2) The anchorage requirements on development length of strand In the ACI Provisions preyed to be a standard to determine a failure pattern within the limited test results of the shallow U-type beams. 3) Those all shear crackings developed from the end of the beams did not lead to anchorage failure. However, initiated strand slip may leads the bond failure by increasing the size of diagonal shear crackings. 4) The flexural mild reinforcement around the vertical center of beam section was effective for developments of a ductile failure.

• Journal of KIISE
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• v.42 no.4
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• pp.468-474
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• 2015

Corporations should make efforts to recognize the importance of projects, identify their failure factors, prevent risks in advance, and raise the success rates, because the corporations need to make quick responses to rapid external changes. There are some previous studies on success and failure factors of projects, however, most of them have limitations in terms of objectivity and quantitative analysis based on data gathering through surveys, statistical sampling and analysis. This study analyzes the failure factors of projects based on data mining to find problems with projects in an audit report, which is an objective project evaluation report. To do this, we identified the texts in the paragraph of suggestions about improvement. We made use of the superior classification algorithms in this study, which were NaiveBayes, SMO and J48. They were evaluated in terms of data of Recall and Precision after performing 10-fold-cross validation. In the identified texts, the failure factors of projects were analyzed so that they could be utilized in project implementation.

• The Journal of Engineering Geology
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• v.20 no.1
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• pp.13-23
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• 2010

Toppling failure of a slope is defined as failure behavior accompanying the rotation of rock block which is different from other failure such as sliding along with discontinuities and so on. It generally occurs in the region that discontinuities were developed with inverse dip direction to a slope and it could play a critical role in judging stability of slope. In this study, the stability evaluation was performed about toppling failure on a jointed road cut-slope. To check the deformation behavior, numerical analysis is widely used. However common analysis programs are based on continuum model. Recently, many methods that discontinuity properties can be considered in continuum analysis are suggested. In this study, numerical analysis based on FEM(Finite Element Method) was performed using interface element applied in heterogeneous boundary to simulate effects of discontinuities.