• 대한기계학회논문집
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• 제6권2호
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• pp.107-112
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• 1982

In order to analyze and investigate in the fatigue behavior of the notched specimens under the two level stressing, the U-notched specimens of structural carbon steel which is generally used is prepared. The obtained results are summarized as follows; (1) The fatigue limit of the U-notched specimens is lower than that of the unnotched. The fatifue notch factor (.betha.) of the U-notched specimens is 1.44 for mild steel and 1.52 for harden steel. The notch sensitivity (q) is 0.68 for mild steel and o.8 for harden steel. That is, these facts show that harden steel is more sensitive to the notch than mild steel. (2) The fatigue life time of the U-notched specimens under the overstressing is shorter than under the constant stressing, and the degree of fatigue life time decrease is different to each stress level; the degree for the high stress level is more than for the low stress level. (3) The fatigue life time of the U-notched specimes under the understressing is longer than under the constant stressing, and the degree of fatigue life time increase for the low stress level is more than for the high stress level.

• 한국산업보건학회지
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• 제18권1호
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• pp.20-31
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• 2008

A respirator is useful to protect a worker from the harmful gases and vapors in the workplace, and the evaluation of respirator cartridge service life is important for the worker's health and safety. The performance of cartridge is effected by several factors such as concentration of gas and vapor, humidity, temperature, adsorbents and cartridge packing density. Adsorption model was applied to both sampling tube and respirator cartridge to predict the service life for organic vapors. The variables of the adsorption model were measured from the experiment with the sampling tube, and it was used to predict the service life of respirator cartridge. In the experiment, we used carbon tetrachloride as a organic vapor and activated carbon take out respirator cartridge as activated carbon. As a result, it was possible to predict the service life of respirator cartridge and predicted service life was quite correct. Breakthrough time decreased with increase of CCl4 concentration. In case of sampling tube, adsorbed amount of CCl4 was larger than respirator cartridge due to linear velocity. Also, rate constant of sampling tube was larger than respirator cartridge, because of, effect of flow rate, packing density. In the prediction of service life of respirator cartridge by using sampling tube, the time required for 50% contaminant breakthrough(${\tau}$) is more effective than the rate constant(k').

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1997년도 추계학술대회 논문집
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• pp.360-363
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• 1997

The method of estimating life time of epoxy composites which be widely used for transformers has been studied in this paper. The breakdown properties of specimens are observed by appling high AC voltage at the room temperature from a series of the experiments. Afterwards, the breakdown time was determined under the constant voltage below the lowest breakdown voltage. Also, V-t properties were found out using weibull distribution widely used in the applications of discrete data for estimating life time of epoxy composites and life exponent n was gained properly. when life exponent is gained is found out, the tong breakdown life time at used voltage can be estimated from breakdown experiments in short time using reverse law of n power.

• 한국컴퓨터정보학회논문지
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• 제24권6호
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• pp.175-182
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• 2019

This study aims to identify causal variables by examining the mutual influences of community consciousness and life satisfaction. We used some data of KCYPS. A longitudinal study of 1952 adolescents selected as a sample was conducted using the Aautoregressive crossover delay model. The results of this study are as follows: First, it showed that life satisfaction is consistently affecting the later life satisfaction with the passage of time. Second, community consciousness showed that the previous community consciousness has a constant influence on the subsequent community consciousness as time passes. Third, the effect of previous life satisfaction on community consciousness was significant. Therefore, the cross-delay effect of life satisfaction on community awareness was stable with time. In other words, life satisfaction level was a causal variable that takes precedence over community consciousness, and the higher the life satisfaction of the previous time, the higher the level of community consciousness in the future. Fourth, the cross-delay effect of community consciousness on life satisfaction was not significant because community consciousness at previous time had no meaningful effect on life satisfaction at later time, so consciousness of community at previous time affects life satisfaction. This study provided some implications basing on this results.

• 품질경영학회지
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• 제27권3호
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• pp.79-93
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• 1999

The common accelerated life test(ALT) consists of test methods applying a constant stress, higher than the use condition stress, to items. There we, however, situations for which a progressive stress ALT, in which the stress on a test item is continuously increased with time, Is more convenient to perform testing and simpler in analyzing data than a constant stress ALT. When a product under constant stress s follows a Weibull distribution with parameters $\theta$(5) and $\beta$, maximum likelihood(ML) estimators of parameters involved in the model are obtained and their asymptotic distributions are derived under stress bounded ramp tests in which the stress is increased linearly from use condition stress to the stress upper bound. The optimum test plans are also found which minimize the asymptotic variance of the ML estimator of the log mean life at design constant stress. For selected values of the design parameters, tables useful for finding optimal test plans are given. The effect of the pre-estimates of design parameters is studied.

• 대한산업공학회지
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• 제20권2호
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• pp.3-17
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• 1994

This paper presents an EMQ model which determines an optimal manufacturing lot size in an unreliable machine. The machine has an exponentially distributed life time, and requires a constant time to repair when it fails. We 1) derive an average cost function, 2) obtain an optimal lot size and show that it is unique, 3) carry out sensitivity analysis to examine the effect of machine parameters (life time, time to repair) to optimal lot size.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 추계학술대회 논문집
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• pp.437-440
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• 2000

In this study, the interfacial dielectric breakdown phenomenon of interface between Epoxy and Rubber was discussed, which affects the stability of insulation system of power delivery devices. The breakdown strength of specimens are observed by applying high AC voltage at the room temperature. The breakdown times under the constant voltage below the breakdown voltage were gained. As constant voltage is applied, the breakdown time is proportion to the breakdown strength. The life exponent n is gained by inverse power law and the long time breakdown life time can be evaluated.

• 품질경영학회지
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• 제24권4호
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• pp.14-28
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• 1996

We consider optimal designs of partially accelerated life testing which is deviced for parallel systems with the considerably long life time. In partially step-stress life testing, test items are first run simultaneously at use condition for a specified time, and the surviving items are then run at accelerated condition until a predetermined censoring time. In partially constant-stress life testing, test items are run at either use or accelerated condition only until a specified censoring time. The optimal criterion for each test is to minimize either the generalized asymptotic variance of maximum likelihood(ML) estimators of the hazard rates at use condition and the acceleration factors or the asymptotic variance of the ML estimators of the acceleration factors.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 춘계학술대회 논문집 유기절연재료 방전 플라즈마
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• pp.46-49
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• 2000

This paper studied development of the program for estimation the life time of insullating materials and the longtime breakdown voltage. First, short-time breakdown voltage of Epoxy and insulating oil was measured. Life exponent was gained from measurement of insulating breakdown time of the specimens. Life time is presumed from program. The estimation program is based on the "Inverse Power Law", defined $V^nt$ is constant. After gaining the life exponent n, it is mapping the longtime breakdown voltages. On the base of life exponent, the estimation the lifetime and usefulness of the insulation systems are possible, furthermore easy calculation is possible.

• 품질경영학회지
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• 제23권1호
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• pp.41-49
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• 1995

This paper suggests optimal accelerated constant stress life tests in Exponential distribution. The relationship between the log-mean life and the loaded stress is assumed to be linear. Optimal plans considering mean square errors of maximum likelihood estimators of the log mean life and test costs are obtained. We consider accelerated life tests with two stress levels, and as data types, failure censoring( type II) and time censoring(type I) data are used. We propose the procedure to obtain the optimal plans for each case. Some examples are also included.