• 한국기계가공학회지
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• 제5권2호
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• pp.42-48
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• 2006

In order to assess the validity of fatigue crack arrest design charts obtained from our previous numerical approach to fatigue crack arrest condition, an extensive fatigue crack growth/arrest test was performed using CT-type integrally stiffened panels. The results are presented as fatigue crack growth rate and non-dimensional crack length relationship, and these are compared with numerically simulated crack growth rates. The measured values of da/dN at the moment of fatigue crack arrest occurred in stiffened panels are good agreement with those numerically simulated crack growth rates.

• 한국세라믹학회지
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• 제37권7호
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• pp.625-631
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• 2000

In this study, the characteristics and sinterablities of TiO2 powders which were fabricated on sol-gel process and supercritical fluid process were examined. The powders fabricated on sol-gel process were amorphous. The particle size and shape were changed with the amount of water used for hydrolysis of titanium ethoxide. The powders were changed from amorphous to crystalline by heating at 400℃. The crystalline anatase TiO2 powders were directly prepared in ethanol supercritical fluid condition that temperature was 270±3℃ and pressure was 7.3 MPa. It's primary crystalline size was 20 nm and agglomerated as spherical shape whose size was 0.7∼1㎛. The powders prepared on sol-gel process were not sintered densely at 900℃ because of abnormal grain growth. However, the powders which prepared on supercritical fluid process were sintered densely at the comparatively low temperature of 800℃ by ideal growth of grain, which are fired at 900℃.

• 한국결정성장학회지
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• 제25권6호
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• pp.231-238
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• 2015

사파이어 단결정은 GaN계 화합물 증착이 용이하여 고휘도 LED(Light Emitting Diode), 고출력 레이저 산업 등에서 크게 각광받고 있다. 다양한 사파이어 단결정 제조공법 중 vertical Bridgman 공법은 고품질의 사파이어를 c-축 방향으로 성장시킬 수 있는 공법이며 상업적으로 적용이 검토되고 있다. 본 연구에서는 2인치 사파이어 성장 vertical Bridgman 공정에서 성장시 온도구배에 의해 발생하는 열응력을 유한요소 모델을 통해 분석하였다. 이를 통해 성장시 수직, 수평방향으로의 온도구배가 사파이어 결정의 열응력과 결함발생에 미치는 영향을 검토하였다.

• 시스템엔지니어링학술지
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• 제16권2호
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• pp.87-96
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• 2020

In this paper we proposed the test design method of reliability growth management. First, we presented the process for establishing the reliability growth management test design considering the number of failures and the termination test time. Reliability growth analysis of continuous system was performed in accordance with the test design process presented. In case the reliability test result is not met with the reliability target value after more than three failures occurred, the required test times were analyzed that 1,725 hrs for one corrective action, 1,950 hrs for two corrective actions. If the number of failures is less than three, design a reliability demonstration test according to confidence level 80% and 90% was performed using RGA 11 Software. As a result, it is possible to establish the reliability growth management test design with sufficient use of available resources. The results of this study can be used when establishing a test design for assessment of reliability growth management of all continuous systems.

• 한국결정성장학회지
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• 제27권3호
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• pp.105-109
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• 2017

고주파 유도 가열 장치를 이용하여 승화법으로 성장된 AlN 단결정을 질소 분위기 하에서 $1200^{\circ}C$와 $1500^{\circ}C$에서 열처리하였다. 열처리 후 단결정 시편들의 표면을 광학현미경으로 관찰하였으며, DCXRD(Double crystal X-ray Diffractometry)를 이용하여 FWHM(Full width of half maximum) 값을 측정하여 결정성의 변화를 평가하였다.

• Journal of Plant Biology
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• 제30권2호
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• pp.135-149
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• 1987

An experiment was made in order to analyze the growth characteristics and productivity of Zoysia japonica under control, mowing and TIBA treatment conditions at the experimental farm of Kyung Hee University. The field was planned by the split plot design method and each treatment was given to two plots (40$\times$40 and 100$\times$100 mm) and was replicated three times. Each plot was 9$m^2$ for Zoysia japonica. The sampling of each plot was taken once a week after sowing. In order to know the dry matter of total standing crops, each organ of plants was kept at 9$0^{\circ}C$ and weighed. Total leaf area of a plant was measured by drawing method. The author adopted the growth analysis of English School. Holocellulose analysis by sodium chlorite method was made. The increasing rate of LAI was high in all plots between 10th and 12th week after sowing and high growth rate of assimilatory organ was observed in low density area of TIBA plot. Between 10th and 12th week after sowing all the experimental plots showed high increasing rate of standing crop and in the process of growth each density area of TIBA plot recorded high increasing rate. In all the plots F/C ratio and RGR were high when the growth rate of assimilatory organ was increasing cosiderably, and the higher the planting density was, the higher F/C ratio was recorded. In all the plots NAR recorded maximum rate before the growth period to show a high increase of RGR. In the process of the growth TIBA plot showed high icnreasing rate of NAR. CGR showed high value in high density areas of all the plots and reached its maximum in the 13th week after sowing. Compared to the other experimental areas the low planting density areas of control plot and TIBA plot showed considerable earlier lignification indicating low Holocellulose content in the growth process.

• 한국신뢰성학회지:신뢰성응용연구
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• 제15권2호
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• pp.90-100
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• 2015

Reliability growth rate (or reliability growth curve slope) have the two cases of trend as a constant or changing one during the reliability growth testing. The changing case is very common situation. The reasons of reliability growth rate changing are that the failures to follow the NHPP (None-Homogeneous Poisson Process), and the solutions implemented during test to break out other problems or not to take out all of the root cause permanently. If the changing were big, the "Goodness of Fit (GOF)" of reliability growth curve to test data would be very low and then reduce the accuracy of assessing result with test data. In this research, we are using Duane model and AMSAA model for assessing test data and projecting the reliability level of complex and repairable system as like construction equipment and vehicle. In case of no changing in reliability growth rate, it is reasonable for reliability engineer to implement the original Duane model (1964) and Crow-AMSAA model (1975) for the assessment and projection activity. However, in case of reliability growth rate changing, it is necessary to find the method to increase the "GOF" of reliability growth curves to test data. To increase GOF of reliability growth curves, it is necessary to find the proper parameter calculation method of interesting reliability growth models that are applicable to the situation of reliability growth rate changing. Since the Duane and AMSAA models have a characteristic to get more strong influence from the initial test (or failure) data than the latest one, the both models have a limitation to contain the latest test data information that is more important and better to assess test data in view of accuracy, especially when the reliability growth rate changing. The main objective of this research is to find the parameter calculation method to reflect the latest test data in the case of reliability growth rate changing. According to my experience in vehicle and construction equipment developments over 18 years, over the 90% in the total development cases are with such changing during the developing test. The objective of this research was to develop the newly assessing method and the process for GOF level increasing in case of reliability growth rate changing that would contribute to achieve more accurate assessing and projecting result. We also developed the new evaluation method for GOF that are applicable to the both models as Duane and AMSAA, so it is possible to compare it between models and check the effectiveness of new parameter calculation methods in any interesting situation. These research results can reduce the decision error for development process and business control with the accurately assessing and projecting result.

• 대한기계학회논문집A
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• 제24권8호
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• pp.2074-2082
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• 2000

In this study, to investigate and to predict the crack growth behavior under variable amplitude loading, crack growth tests are conducted on 7075-T6 aluminum alloy. The loading wave forms are generated by normal random number generator. All wave forms have same average and RMS(root mean square) value, but different standard deviation, which is to vary the maximum load in each wave. The modified Forman's equation is used as crack growth equation. Using the retardation coefficient D defined in previous study, the load interaction effect is considered. The variability in crack growth process is described by the random variable Z which was obtained from crack growth tests under constant amplitude loading in previous work. From these, a statistical model is developed. The curves predicted by the proposed model well describe the crack growth behavior under variable amplitude loading and agree with experimental data. In addition, this model well predicts the variability in crack growth process under variable amplitude loading.

• 대한환경공학회지
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• 제27권2호
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• pp.206-214
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• 2005

본 연구는 도시하수 처리시 부유성장 미생물만을 이용하는 표준 활성슬러지 공정(Conventional Activated Sludge; CAS) 및 MLE(Modified Ludzack-Ettinger) 공정과 부유 및 부착 미생물을 동시에 활용하는 하이브리드(hybrid)형 공정인 M-Dephanox(Modified-Dephanox) 공정의 유기물, 질소 및 인 제거효율을 상호 비교 검토하고자 하였다. M-Dephanox 공정은 기존 Dephanox 공정의 단점을 극복하기 위하여 고안된 공정으로서 기존 Dephanox 공정에 비해 탈질 효율을 증가시킬 수 있다. 연구 결과 부유 성장 미생물을 이용하는 MLE 공정에 비해 하이브리드형 공정인 M-Dephanox 공정의 TCOD, T-N 및 T-P 제거효율이 각각 12.3, 18.6, 28.2% 더 높게 관찰 되었다. M-Dephanox 공정이 MLE 공정에 비해 유기물 및 질소 제거 효율이 더 높은 원인은 M-Dephanox 공정이 하이브리드 공정이자 다단 슬러지 공정(multi-sludge)인 동시에 생흡착(biosorption)을 이용한 효과적인 유기물 이용 기작이 있기 때문이다. M-Dephanox 공정의 질산화 반응조에서의 암모니아성 질소 제거효율은 약 2hr의 수리학적 체류시간에서 약 96.7%로 나타나 Dephanox 공정과 관련한 기존 문헌에서 보고된 5 hr의 체류시간 보다 3 hr 짧은 수리학적 체류시간에서도 높은 암모니아성 질소 제거효율을 관찰 할 수 있어 전체 공정의 수리학적 체류시간을 줄이는데 커다란 역할을 할 것으로 기대된다.

• International Journal of Reliability and Applications
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• 제4권1호
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• pp.1-12
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• 2003

Many software reliability growth models (SRGM's) based on a nonhomogeneous Poisson process (NHPP) have been proposed by many researchers. Most of the SRGM's which have been proposed up to the present treat the event of software fault-detection in the testing and operational phases as a counting process. However, if the size of the software system is large, the number of software faults detected during the testing phase becomes large, and the change of the number of faults which are detected and removed through debugging activities becomes sufficiently small compared with the initial fault content at the beginning of the testing phase. Therefore, in such a situation, we can model the software fault-detection process as a stochastic process with a continuous state space. In this paper, we propose a new software reliability growth model describing the fault-detection process by applying a mathematical technique of stochastic differential equations of an Ito type. We also compare our model with the existing SRGM's in terms of goodness-of-fit for actual data sets.