• Proceedings of the KSME Conference
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• 2004.11a
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• pp.7-12
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• 2004

A lifetime prediction of holddown spring screw in nuclear fuel assembly was performed using fracture mechanics approach. The spring screw was designed such that it was capable of sustaining the loads imposed by the initial tensile preload and operational loads. In order to investigate the cause of failure and to predict the stress corrosion cracking life of the screw, a stress analysis of the top nozzle spring assembly was done using finite element analysis. The elastic-plastic finite element analysis showed that the local stresses at the critical regions of head-shank fillet and thread root significantly exceeded than the yield strength of the screw material, resulting in local plastic deformation. Normalized stress intensity factors for PWSCC life prediction was proposed. Primary water stress corrosion cracking life of the Inconel 600 screw was predicted by using integration of the Scott model and resulted in 1.78 years, which was fairly close to the actual service life of the holddown spring screw.

• Journal of Applied Reliability
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• v.4 no.2
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• pp.121-131
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• 2004

HALT (Highly Accelerated Life Test) was performed to improve the reliability by removing the potential failure for newly developing PCB used for the vibration condition from 2OHz to 2OOHz. During HALT, it is found that the lead of Al electrolytic capacitor of SMD type is detached from PCB. As the result for the failure analysis and FEM (Finite Element Method), it is clarified that the root cause for this failure is the improper attachment of an Al electrolytic capacitor on PCB by the mistake of a PCB design. HALT was performed in previous condition to verify the failure analysis after molding an epoxy resin to overcome the PCB design mistake and it is not observed the same failure. Therefore, it is assumed that the same failure in field will be not occurred by the proper implementation.

• Korean Journal of Construction Engineering and Management
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• v.25 no.4
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• pp.66-81
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• 2024

Identifying the root causes of substandard construction projects is crucial considering the social and economic issues structural failures can cause. To date, the focus has predominantly been on identifying and penalizing the culprits rather than uncovering the fundamental reasons. Therefore, this study aims to identify various factors that contribute to failures in construction project quality management, including aspects of substandard construction projects, and determine the relationship between these factors and substandard construction projects. Through a literature review and case analysis, 61 influential factors were identified. A survey targeting participants including structural designers, architectural designers, construction companies, CM, and researchers was conducted to gauge the consensus on these factors. A regression analysis was performed based on data from 724 survey respondents. Ultimately, based on the 17 key influencing factors identified by the regression analysis, 9 preventive measures against substandard construction projects were proposed. This study is significant as it elucidates the reasons behind construction project quality management failures that lead to substandard construction projects and establishes a framework for developing practical solutions to real-world problems rather than theoretical or abstract ones.

• Journal of Power System Engineering
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• v.11 no.1
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• pp.5-15
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• 2007

In the recently released accident-investigation report on blade failure, almost 70% of blade failures was found at low pressure turbine blades, and it is well known that main cause is due to the vibration modes. This paper describes the systematic approach on the root cause of the blade failure at L 0 stage, 30MW single flow industrial steam turbine which had tripped by high vibration after ten-month commercial operation. A fracture was found at the only one damping wire hole of 59 blades, and crack was detected at three damping wire holes by NDT. According to the analysis result for the crack fracture surface and the chain of the sequential operational events, we come to the conclusion that a typical high cycle fatigue is the most dominant factor caused to the blade failure, the resonance frequency margin was narrowed by the cut damping wire and the high cycle vibration was amplified, and then the blade was broken at once by the centrifugal force when the crack reached the critical size.

• Journal of Drive and Control
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• v.15 no.4
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• pp.48-54
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• 2018

The hydraulic servo actuator has always operated very precisely with high frequency and small displacement, and is used continuously for a long time. The hydraulic servo actuator of the test equipment used in the accelerated life test in order to guarantee the service life of the automotive parts failed earlier than the products before finishing the test. This study performed an analysis on the cause of the failure of the hydraulic servo actuator used in the test equipment, changed the design of the actuator to solve the root cause of the main failure mode, and developed the improved servo actuator. Based on above process, this study established a better performances and longer lifetime of the servo actuator after testing.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.136-141
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• 2004

The gear in various mechanical components easily occurs at damages by the external torque. The main failure modes of the gear are surface pitting with the tooth surface and breakage with tooth root by caused fatigue. Therefore, the gear is very important role in the reliability research since it may cause fatal damage of entire system such as the gear box in automobile transmission. In this study, the failure mode of the gear was analyzed and accelerated durability analysis was employed for the life estimation of spur gears. In the case of assumed load spectrums, the reliability of spur gears was evaluated by inverse power law-Weibull accelerated life test model with cumulative damage exposure.

• Proceedings of the KSR Conference
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• 2009.05a
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• pp.1817-1827
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• 2009

Although human error is recognized as the primary cause of railway accidents and incidents, there have been limitations in finding the root causes of errors and developing effective corrective actions in the Korean railway industry, due to the absence of a systematic method and lack of professional knowledge and skills of investigators. Therefore, there has been a strong need for a systematic methodology for human error analysis. This paper introduces a methodology for analyzing human error m railway operations, called HEAR (Human Error Analysis and Reduction). HEAR is intended to help analysts identify the sequences and various levels of causes of operators' erroneous actions in railway accidents or incidents and make recommendations to eliminate or reduce the future possibility of similar errors and accidents. It was developed based on a thorough investigation of various techniques for human errors analysis and feedback from field investigators.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.1722-1730
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• 2007

According to the result of recent studies, it was revealed that the error of safety-related personnel still plays a significant role in the accidents and/or incidents of a railway system. Accordingly, in order to reduce as well as prevent human errors, it is necessary to: (1) identify the root cause of accidents/incidents, and (2) conduct a research that can provide a systematic as well as an effective way to deal with the identified human errors. To this end, it is essential to suggest appropriate countermeasures based on the result of a task load analysis, which can soundly reduce a high level of the task load put on safety-related personnel. In the light of this concern, about the tasks of railway traffic signallers, a detailed task analysis was conducted in this study. After that, the associated task load scores were quantified by NASA-TLX technique that is one of the most well-known subjective workload measurement techniques. As a result, a set of significant tasks that could put a high task load on railway traffic signallers was identified.

• The Plant Pathology Journal
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• v.33 no.3
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• pp.249-263
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• 2017

This study aims to examine the potential reasons for the current prevalence of the fusarium wilt in the oriental melon. Twenty-seven Fusarium isolates obtained from oriental melon greenhouses in 2010-2011 were identified morphologically and by analysis of elongation factor-1 alpha gene (EF-$1{\alpha}$) and internal transcribed spacer (ITS) rDNA sequences as 6 Fusarium species (8 isolates of F. oxysporum, 8 F. commune, 5 F. proliferatum, 3 F. equiseti, 2 F. delphinoides, and 1 F. andiyazi), which were classified as same into 6 EF-$1{\alpha}$ sequence-based phylogenetic clades. Pathogenicity of the Fusarium isolates on the oriental melon was highest in F. proliferatum, next in F. oxysporum and F. andiyazi, and lowest in the other Fusarium species tested, suggesting F. proliferatum and F. oxysporum were major pathogens of the oriental melon, inducing stem rots and vascular wilts, respectively. Oriental melon and watermelon were more susceptible to F. oxysporum than shintosa and cucumber; and cucumber was most, oriental melon and watermelon, medially, and shintosa was least susceptible to F. proliferatum, whose virulence varied among and within their phylogenetic subclades. Severe root-knot galls were formed on all the crops infected with Meloidogyne incognita; however, little indication of vascular wilts or stem and/or root rots was shown by the nematode infection. These results suggest the current fungal disease in the oriental melon may be rarely due to virulence changes of the fusarium wilt pathogen and the direct cause of the severe root-knot nematode infection, but may be potentially from other Fusarium pathogen infection that produces seemingly wilting caused by severe stem rotting.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.1
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• pp.54-63
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• 2022

The Marine Accident Investigation and Tribunal System is intended to provide a credible solution to prevent the recurrence of similar accidents. When a marine accident occurs, the Korea Maritime Safety Tribunal seeks to find its root causes through an analysis of what provoked the accident. It also contributes to the development of safety policies or practices by making a decision based on the findings. However, if the decision presented as the root cause of a marine accident is ambiguous or unclear, it may be difficult to achieve its intended goal. Hence, if we read some of the decisions of the Maritime Safety Tribunal, it is selective to directly apply the cause of an accident as a source of the measures that can prevent its recurrence. A typical example of this is the expression: "when a seafarer neglects ordinary practice of seaman." The term "ordinary practice of seaman" has been criticized for being used in some decisions like a master key where it is not easy to determine which specific rules or regulations were violated or blame the involved seafarers. Such term is present in Article 2 of the International Regulations for Preventing Collisions at Sea 1972. For the proper use of the term, this paper seeks to compare and establish the concepts of "ordinary practice of seaman" and the duty of care by providing a systematic interpretation of the original text. In addition, the duty of care was reviewed from the perspective of administrative, civil, and criminal laws. Furthermore, relevant legal precedents were reviewed and presented in the study. Accordingly, it is expected that the term "ordinary practice of seaman" would be properly used in decisions that contribute to the prevention of the recurrence of similar marine accidents.