• 산업기술연구
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• 제28권B호
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• pp.157-165
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• 2008

Level II AFDA and Level III MCS reliability models are applied to analyze the stability of armor units on trading and coastal harbors in Korea. Hudson's formula and Van der Meer's formula are used in this reliability analysis. Also, probability density functions of reliability index and probability of failure are derived by the additional analysis. In addition, the partial safety factors of all harbors related to armor units can be straightforwardly evaluated by the inverse-reliability method. The upper and lower limits and average level of partial safety factors can be statistically investigated with the results of all cases applied in this paper. Therefore, it may be possible to design armor units of new breakwaters including the uncertainty of random variable and target level by using the present results.

• 대한전기학회논문지:전력기술부문A
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• 제48권9호
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• pp.1073-1080
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• 1999

Optimal routing of distribution networks can be attained by keeping the line power capacity limit to handle load requirements, acceptable voltage at customer loads, and the reliability indices such as SAIFI, SAIDI, CAIDI, and ASAI limits. This method is composed of optimal loss reduction and optimal reliability cost reduction. The former is solved relating to the conductor resistance of all alternative routes, and the latter is solved relating to the failure rate and duration of each alternative route. The routing considering optimal loss only and both optimal loss and optimal reliability cost are compared in this paper. The case studies with 10 and 24 bus distribution networks showed that reliability cost should be considered as well as loss reduction to achieve the optimal routing in the distribution networks.

• International Journal of Reliability and Applications
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• 제10권2호
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• pp.109-118
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• 2009

Crankshaft, the core element of the engine of a vehicle, transforms the translational motion generated by combustion to rotational motion. Its failure will cause serious damage to the engine so its reliability verification must be performed. In this study, the S-N data of the bending and torsion fatigue limits of a crankshaft are derived. To evaluate the reliability of the crankshaft, reliability verification and analysis are performed. For the purpose of further evaluation, the bending and torsion tests of the original crankshaft are carried out, and failure mode analysis is made. The appropriate number of samples, the applied load, and the test time are computed. On the basis of the test results, Weibull analysis for the shape and scale parameters of the crankshaft is estimated. Likewise, the $B_{10}$ life under 50% of the confidence level and the MTTF are exactly calculated, and the groundwork for improving the reliability of the crankshaft is laid.

• 한국정밀공학회지
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• 제27권9호
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• pp.78-85
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• 2010

Creep characteristic is an important failure mechanism when evaluating engineering materials that are soft material as polymers or used as mechanical elements at high temperatures. One of the popular thermo-elastic polymers, Polycarbonate(PC) which is used broadly for engineering polymer, as it has excellent mechanical and thermal properties compared to other polymers, was studied for creep characteristic at various level of stresses and temperatures. From the experimental results, the creep limit of PC at room temperature is 85 % of tensile strength. which is higher than PE (75%)at room temperature. Also the creep limits decreased exponentially as the temperatures increased, up to 50 % of the melting point($267^{\circ}C$). Also the first and third stage among the three creep stages was non-existent nor was there any rupture failure which occurred for many metals.

• Tribology and Lubricants
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• 제15권4호
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• pp.328-334
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• 1999

Acoustic emission (AE) sensor was used to evaluate the wear-life of CrN-coated steel disks with 1 $\mu\textrm{m}$ and 4 $\mu\textrm{m}$ coating thickness. The relationship between Af and friction signal from scratch test and sliding test was investigated. The first spatting of CrN film was detected by AR signals in the early stage of coating failures, and overall failures by friction signals. Therefore, the conservative design for coating-life should be done using the results of AE signals. Using the percent contact load, the ratio of sliding normal load to the critical scratch load and the number of cycles to failure was measured to predict the wear-life of CrN film. On the wear-life dia-gram the percent contact loads and the number of cycles to failure showed a good linear relationship on the log coordinate. As the load percentage was decreased, the diagram showed that the wear-limits, at which the coated steels survived more than 35,000 cycles, were about 4∼5% of the critical scratch loads.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(I)
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• pp.251-254
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• 2005

A number of studies have been conducted on FRP shear strengthening of RC beams during the past decade. The test results indicated. that the strengthened specimens failed predominantly by debonding of the FRP sheets before reaching the rupture strength of FRP sheets. For this reason, limits on the effective strain in FRP have been incorporated in ACI 440.2R recommendation considering debonding failure. This paper presents the test results of 7 small scale RC beams shear-strengthened with glass fiber sheets. Three types of FRP configurations, such as two sides bonded, U wrap and fiber shear-key embedded, were considered. GFRP sheet were bonded vertically to member axis along the shear span. From the test results, it was found that debonding strain of GFRP sheets at failure decreased with the number of layers. In addition, effective strain of FRP proposed by ACI 440.2R recommendation has been verified in this study.

• 산업경영시스템학회지
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• 제21권45호
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• pp.319-328
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• 1998

In this paper, the design of ALT(Accelerated Life Test) requires a sampling plan based on failure-censored(Type II censored) ALT with lognormal life distribution. Specially the environmental effect of products has been emphasized, so we considered the upper life limit as well as lower life limit in the ALT sampling plan. The optimal plan with a high stress and a low stress is used as test plan, and the total sample size for test and lot acceptability constant which minimize an asymptotic variance of maximum likelihood estimator of assumed model parameters and satisfy the given producer's risk and customer's risk are drawn out. These values can be acquired by means of the computer program that we coded for resolving the difficulty and complexity of calculation.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2006년도 추계학술대회 논문집
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• pp.80-84
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• 2006

Fracture mechanics approach can be severly hampered unless considerable detailed specific knowledge is available. The problem of railway wheel-rail system fatigue design is currently undertaken by using assumed conservative design procedures. However, although the failure rate is low, the consequences of any such failure can be far reaching. It has been demonstrated that the tools available for effective management have limits. In the present study, the safety evaluation based on fracture mechanics is carried out. The critical crack size and remaining lifetime are calculated on the wheel for high-speed train.

• 한국안전학회지
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• 제8권1호
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• pp.64-70
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• 1993

Serious injuries and deaths due to multi-jointed robot occur when a man mispercepts. especially during robot teaching and maintenance work. Since industrial robots often operate with unpredictable motion patterns, establishment of safe speed limit of robot arm is indispensable. An experimental emergency conditions were simulated with a multi-jointed robot. and response characteristics of human operators were measured. The result showed that failure type, robot arm axis. and robot arm speed had significant effects on human reaction time. The reaction time was slightly increased with robot arm speed. though it showed somewhat different pattern owing to failure type. Furthermore the reaction time to the axis which could flex or extend. acting on a workpiece directly. was fastest and its standard deviation was small. The robot arm speed limit securing a‘possible contact zone’based on overrun distance was about 25cm/sec. and in this sense the validity of safe speed limits suggested by many precedent researchers were discussed.

• 한국정밀공학회지
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• 제28권12호
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• pp.1403-1410
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• 2011

Creep characteristic is an important failure mechanism when evaluating engineering materials that are soft material as polymers or used as mechanical elements at high temperatures. One of the popular thermo-elastic polymers, Polymethyl methacrylate(PMMA) which is used broadly for engineering polymer, as it has excellent mechanical and thermal properties compared to other polymers, was studied for creep characteristic at various level of stresses and temperatures. From the experimental results, the creep limit of PMMA at room temperature is 85 % of tensile strength. which is higher than that of PE (75%)at room temperature. Also the creep limits decreased to nil linearly as the temperatures increased, up to $120^{\circ}C$ of the melting point($267^{\circ}C$). Also the first and third stage among the three creep stages were non-existent nor were there any rupture failure which occurred for many metals at high temperatures.