• Korean Journal of Materials Research
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• v.4 no.3
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• pp.349-356
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• 1994

For the deformation, life time prediction and improvement of the life time in high temperature materials it's very important to know the mechanism of deformation. For these mechanisms the dislocation loop models of Orlova et al. and Mills et al. are used often now. But they show controversial differencies, even if they have unertaken similar experimental tests with the same alloy of A1-5.5at.% Mg. In this work also the similiar tests of them have done under the same temperature of 573 K ; (1) The specimen was deformed by $\sigma$= 30MPa and $\varepsilon$=0.03. (2) Direct after creep deformation of $\sigma$= 30MPa and $\sigma$= 0.03 the stress reduction tests to 15, 10 and OMPa have been performed. (3) To study the loop models dislocation structure and dislocation density ( p ) have been observed.

• Journal of Digital Contents Society
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• v.16 no.1
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• pp.63-70
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• 2015

In this paper, we estimate the life cycle from acceleration life test about the hard disk of disk array of image storage of PACS. Webuil distribution was selected by the Anderson-Darling goodness-of-fit test with data of down time at $50^{\circ}C$ and $60^{\circ}C$. The equality test of shape parameter and scale parameter was conducted, so that the probability distribution estimated from data of down time at $50^{\circ}C$ and $60^{\circ}C$ was not statistically significant. The shape parameter was 1.0409, The characteristic life was 24603.5 hours at normal user condition($30^{\circ}C$) by the analysis of weibull-arrhenius modeling which included the acceleration factor of temperature, and The activation energy was 0.5011 eV through arrhenius modeling. The failure analysis of the failure samples of acceleration test and the samples of market return was conducted, so that the share percentage of failure mode was detail difference but the rank of share percentage was almost same. This study suggest the test procedure of acceleration test of hard disk drive in PACS using environment, and help the life estimation at manufacture and use.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.8
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• pp.1569-1580
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• 2016

For the 2.4 GHz active RFID to be successful in the market, one of the requirements is the increased battery life. However, currently we do not have any accurate power consumption estimation method. In this study we develop a simulation model, which can be used to estimate power consumption of tag accurately. Six different simulation models are proposed depending on collision algorithm and query command method. To improve estimation accuracy, we classify tag operating modes as the wake-up receive, UHF receive, sleep timer, tag response, and sleep modes. Power consumption and operating time are identified according to the tag operating mode. Query command for simplifying collection and ack command procedure and newly developed collision control algorithm are used in the simulation. Other performance measures such as throughput, recognition time for multi-tags, tag recognition rate including power consumption are compared with those from the current standard ISO/IEC 18000-7.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.10
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• pp.1119-1124
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• 2009

This paper deals with the variability analysis of short term creep rupture test data based on the previous creep rupture tests and the possibility of the creep life prediction. From creep tests performed by constant uniaxial stresses at 600, 650 and $700^{\circ}C$ elevated temperature, in order to investigate the variability of short-term creep rupture data, the creep curves were analyzed for normalized creep strain divided by initial strain. There are some variability in the creep rupture data. And, the difference between general creep curves and normalized creep curves were obtained. The effects of the creep rupture time (RT) and steady state creep rate (SSCR) on the Weibull distribution parameters were investigated. There were good relation between normal Weibull parameters and normalized Weibull parameters. Finally, the predicted creep life were compared with the Monkman-Grant model.

• Transactions of the Korean hydrogen and new energy society
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• v.32 no.6
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• pp.592-611
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• 2021

In this study a rarely available high-throughput cycling data set of 124 commercial lithium iron phosphate/graphite cells cycled under fast-charging conditions, with widely varying cycle lives ranging from 150 to 2,300 cycles including in-cycle temperature and per-cycle IR measurements. We worked out own Python codes which reproduced the various data plots and machine learning approaches for cycle life prediction using early cycles and more details not presented in the article and the supplementary information. Particularly, we applied regularized ridge, lasso and elastic net linear regression models using features extracted from capacity fade curves, discharge voltage curves, and other data such as internal resistance and cell can temperature. We found that due to the limitation in the quantity and quality of the data from costly and lengthy battery testing a careful hyperparameter tuning may be required and that model features need to be extracted based on the domain knowledge.

• Journal of the Korean Ceramic Society
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• v.30 no.3
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• pp.229-235
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• 1993

Thermal history and thermal stress of alumina specimen, which occured from thermal shock process, were calculated by finite difference method. Stress intensity factor and crack growth in cyclic thermal fatigue were calculated from single thermal shock temperature history and thermal stress. Cyclic thermal life were estimated by bending strength after cyclic thermal shock under critical thermal shock temperature. Calculated stress intensity factor was compared with real experimental thermal fatigue life of specimen. Fatigue life until critical stress intensity factor and real experimental result were comparable.

• Journal of the Korean Ceramic Society
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• v.31 no.10
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• pp.1141-1146
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• 1994

Cyclic fatigue experiment was carried out to predict the life time of alumina ceramics. Four kinds of model were suggested to obtain the adequate representative static stress corresponding to the cyclic stress applied to the alumina specimens. Arithmetic mean stress model gives 21.81 of the crack growth exponent, integrated stress model gives 22.15, maximum stress model gives 24.57, and equivalent static stress model gives 24.43. It is considered that the equivalent static stress model is the most reasonable and gives the best adequate crack growth exponents value.

• Proceedings of the Korean Nuclear Society Conference
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• 1995.05a
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• pp.765-770
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• 1995

지체균열전파(DHC)는 중수로 압력관의 수명에 근 영향을 미치는 중요한 현상 중의 하나이다. 본 연구에서는 열처리를 통하여 압력관 재료인 Zr-2,5Nb의 기계적 성질, 집합조직을 변화시켜 각 인자들이 DHC에 미치는 영향을 조사하였다. 그 결과 지체균열전파속도(DHCV)는 항복강도와 경도와 비례한다는 것과 유사한 미세구조와 집합조직을 갖는 Zr-2.5Nb의 경우 항복강도와 Puls의 모델을 이용하여 지체균열전파속도(DHCV)를 예측할 수 있었다. 그리고 secondary cracking이 annealing한 시편들에서는 관찰되었으나 $\beta$열처리 후 급냉한 시편에서는 관찰되지 않았다. 이것의 수소화물 형상의 차이에 의한 것으로 생각된다.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10b
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• pp.731-736
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• 1998

Deteriorations of concrete are governed by combined factors such as environmental stressors, processes and rates of deteriorations. Due to this reason, it's very difficult and important issue to predict quantitatively the service life of concrete structure. From this pont of views, the purpose of this study is to propose the approaches on the further development for predicting the remaining service life of concrete by analyzing the deteriorations mechanism and evaluating the existing models.

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 2002.05a
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• pp.177-183
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• 2002

인명이나 물적 재산에 많은 손실을 가져주는 기계설비 및 구조물의 파괴현상에 대한 연구는 재해 원인을 분석하고 안전대책을 수립하기 위한 측면에서 대단히 중요하며, 지금까지 많은 연구가 행하여져 오호 있다 프랙탈기하학에 대한 연구는 Mandelbrot/sup l)/에 의하여 제안되어 20년 정도의 짧은 기간임에도 불구하고 여러 분야의 자연현상을 모델화하기 위하여 다양하게 발표가 되고 있다. 프랙탈 특성은 자연현상의 불규칙한 변화를 정량적으로 나타내기 위한 프랙탈차원으로 평가된다 프랙탈차원은 파면 및 균열의 불규칙성을 정량화함으로써 균열수명을 보다 더 정확히 예측하는데 적용될 수 있다.(중략)