• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.5
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• pp.769-774
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• 2010

It happened fractures on special bolt which supported main landing gear actuator up-lock rod of aircraft. Cracks were initiated mainly from the center hole and the external thread of the special bolt. To find out failure root causes, metallographic, fractographic analyses as well as test work were carried out. From the fractographic study by SEM work, fracture occurred by a brittle intergranular type failure. The fracture could be occurred primarily by solid-metal-induced embrittlement due to cadmium embrittler penetrated into the flaw existed after machining work for center hole and thread on the bolt during baking treatment processing to eliminate hydrogen. For its successful application, cadmium EP bolts require proper and adequate baking treatment after electroplating, and make no more drilled center hole on the bolt to prevent same failure.

• Journal of the Korean Society of Safety
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• v.34 no.1
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• pp.14-20
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• 2019

This paper presents a safety assessment based approach for the safe operation for PCS(Power Conditioning System) of photovoltaic and energy storage systems, applying FTA. The approach established top events as power outage and a failure likely to cause the largest damage among the potential risks of PCS. Then the Minimal Cut Set (MCS) and the importance of basic events were analyzed for implementing risk assessment. To cope with the objects, the components and their functions of PCS were categorized. To calculate the MCS frequency based on IEEE J Photovolt 2013, IEEE Std. 493-2007 and RAC (EPRD, NPRD), the failure rate and failure mode were produced regarding the basic events. In order to analyze the top event of failure and power outage, it was assumed that failures occurred in DC breaker, AC breaker, SMPS, DC filter, Inverter, CT, PT, DSP board, HMI, AC reactor, MC and EMI filter and Fault Tree was drawn. It is expected that the MCS and the importance of basic event resulting from this study will help find and remove the causes of failure and power outage in PCS for efficient safety management.

• Journal of the Korea Institute of Military Science and Technology
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• v.12 no.6
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• pp.719-726
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• 2009

A delay system in fuze for high explosive shell is an important safety device, but failure in the delay system usually causes failure of the shell. Root-cause analysis of failure in the delay system is required since failure in over 10-years stored delay system recently occurs. In this paper, failure in the delay system was reproduced experimentally to examine aged characteristics of the delay system, and the failed delay system shows the same characteristics as ones of failed delay systems in field. Based on the reproduced experiments, accelerated life testings and the data analysis of failure times of delay systems were performed to predict the storage lifetime.

• 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.

• Korean Journal of Construction Engineering and Management
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• v.13 no.3
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• pp.78-88
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• 2012

Previous construction failure researches were focused on the utilization plan based on failure information and development of failure classification. However, it has limitation to set up the plan for prevention of construction failure due to the lack of the number of on-site staffs. In order to prevent effectively construction failure, a prevention plan should be established through quantitative evaluation of failure causes. The purpose of this study is to suggest the assessment method for selection Critical Management Factor(CMF) and to analyze the CMF on the apartment structural framework using FMEA(Failure Mode and Effective Analysis) which is one of the methods of quantitative evaluation. The element of risk evaluation separated degree of failure risk and prevention respectively. The assessment method for selection of CMF can be utilized for planning proactive solutions on the failure, and it can be also selected critical factors about each project phases, type of facility and construction work.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.2026-2036
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• 1991

An expert system is developed which can diagnose the causes and remedies of the failures of power transmission gears. The basic components of the expert system are knowledge base, inference engine, and working memory. The knowledges in knowledge base are classified into the knowledges for determining the failure types and for diagnosis of causes and remedies of the failures. The former is represented hierarchically into the main category of eleven groups by rules and the sub category of twenty four groups by facts, while the later is represented by facts according to the each group of knowledges. In the inference engine some considerations are implemented, i.e., the backward chaining method and depth first search to determine the category of the failures, the meta-knowledges to shorten the search space, the certainty factor to evaluate the reliability of result, and the unification strategy to diagnose the causes and remedies of the failures. The working memory is established to hold the results during inference temporarily. In addition, knowledge acquisition facility, explanation facility, and user interface are included for the usefulness of user. This expert system is written with the PROLOG programming language on IBM-PC compatible computer operated by MS-DOS and be executed alone.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.660-670
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• 2009

Neighboring construction becomes mainstream of Ground excavation in downtown area. This causes the displacement, deformation, stress condition, etc of the ground surroundings. Therefore Neighboring construction have an effect on Neighboring structure. All these years a lot of Neighboring construction carried out, and the accumulation of technology also get accomplished. But earth retaining structure collapse happens yet. Types of earth retaining structure collapse are 12. 1. Failure of anchor or strut system, 2. Insufficiency of penetration, 3. H-pile Failure on excessive bending moment, 4. Slope sliding failure, 5. Excessive settlement of the back, 6. Deflection of H-pile, 7. Joint failure of coupled H-pile, 8. Rock failure when H-pile penetration is rock mass, 9. Plane arrangement of support systems are mechanically weak, 10. Boiling, 11. Heaving, 12. Over excavation. But field collapses are difficult for classification according to the type, because collapse process are complex with various types. When we consider the 12 collapse field, insufficient recognition of ground condition is 4 case. Thorough construction management prevents from fault construction. For limitations of soil survey, It is difficult to estimate ground condition exactly. Therefore, it should estimate the safety of earth retaining system, plan for necessary reinforcement, according to measurement and observation continuously.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.45 no.3
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• pp.78-89
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• 2022

The purpose of this study was to propose useful suggestion by analyzing preventive replacement policy under which there are minor and major failure. Here, major failure is defined as the failure of system which causes the system to stop working, however, the minor failure is defined as the situation in which the system is working but there exists inconvenience for the user to experience the degradation of performance. For this purpose, we formulated an expected cost rate as a function of periodic replacement time and the number of system update cycles. Then, using the probability and differentiation theory, we analyzed the cost rate function to find the optimal points for periodic replacement time and the number of system update cycles. Also, we present a numerical example to show how to apply our model to the real and practical situation in which even under the minor failure, the user of system is not willing to replace or repair the system immediately, instead he/she is willing to defer the repair or replacement until the periodic or preventive replacement time. Optimal preventive replacement timing using two variables, which are periodic replacement time and the number of system update cycles, is provided and the effects of those variables on the cost are analyzed.

• Geomechanics and Engineering
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• v.34 no.3
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• pp.285-301
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• 2023

During the construction of E75 highway through Grdelica gorge in Serbia, a major failure occurred in the zone of reinforced rock slope. Excavation was performed in highly anisotropic Paleozoic schist rock formation. The reinforcement consisted of the two rows of micropile wall with pre-stressed anchors. Forces in anchors were monitored with load cells while benchmarks were installed for superficial displacement measurements. The aim of the study is to investigate possible causes of instability considering different probability distributions of the strength of discontinuities and anchor bond strength by applying different optimization techniques for finding the critical failure surface. Even though the deterministic safety factor value is close to unity, the probability of failure is governed by variability of shear strength of anisotropic planes and optimization method used for locating the critical sliding surface. The Cuckoo search technique produces higher failure probabilities compared to the others. Depending on the assigned statistical distribution of input parameters, various performance functions of the factor of safety are obtained. The probability of failure is insensitive to the variation of bond strength. Different sampling techniques should yield similar results considering that the sufficient number of safety factor evaluations is chosen to achieve converged solution.

• Journal of Chest Surgery
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• v.25 no.1
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• pp.49-56
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• 1992

Total 20 cases of reoperation for mitral vavular disease, which had been performed during the period from May 1983 till October 1991, were reviewed. This study contained 1 case of previous balloon valvuloplasty and 1 case of death with bleeding from right ventricle during sternal reenrty. The average time intervals between reoperation and previous operation was 19 years in closed mitral commissurotomy[n=4], 7 years and 2 months in mitral valve replacement[n=10], 1 year and 8 months in mitral valvuloplasty[n=4], 3 years and 10 months in open mitral commissurotomy [n=2]. The cause of reoperation in closed mitral commissurotomy was progression of the disease, and residual stenosis with progression was the cause in open mitral commissurotomy cases. Technical failure might be the cause in the cases of valvuloplasty. In prosthetic valve replacement group the causes of reoperation were primary failure. Also two cases of suggested valve thrombosis and one case of failure of tricuspid annuloplasty was noted in prosthetic valve replacement group. The used valves for reoperation were Ionescue-Shiley in 3 cases, Bjork-Shiley in 6 cases, St. Jude Medical in 2 cases and CarboMedics in 8 cases. The mortality rate was 20%[n=4] and the causes of death were low output syndrome in 1 case, multiple organ failure in 2 cases and bleeding in 1 case during sternal reentry. During follow up 1 case of sudden death was observed.