• 연구논문집
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• 통권32호
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• pp.35-43
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• 2002

This study was performed to develop accelerated life test method of machanical parts using cumulative damage theory that used to model the fatigue of parts that receive variable load. The cumulative damage theory was introduced, and the estimation of life and calculation of accelerated life test time was illustrated. As the actual application example, accelerated life test method of agricultural tractor transmission was described. Life distribution of agricultural tractor transmission was supposed to follow Weibull distribution and life test time was calculated under the conditions of average life (MTBF) 3,000 hours and 90% reliability for one test sample. According to the cumulative damage theory, because test time can shorten in case increase test load, test time could be reduced by 482 hours when we put the load 1.1 times of rated load than 0.73 times of rated load that is equivalent load calculated by load spectrum of the agricultural tractor. This time, acceleration coefficient was 11.7. This accelerated test method was used to develop accelerated test method of gear reducer, hydraulic hose and bearing as well as agricultural tractor transmission and it is considered to be applied comprehensively to machanical parts the fatigue of which is happened by load or pressure etc.

• 대한기계학회논문집A
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• 제20권12호
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• pp.3892-3898
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• 1996

In this study, the prediction of the fatigue life as well as the extimation of the characteristics of fatigue cumulative damage on GFRP under random loading were performed. The constant amplitude tests and the ramdom loading test were carried on notched GFRP specimens with a circular hole. Random waves were generated with a micro-computer and had wide band spectra. Since it is useful that the prediction of fatigue life ot the given load sequences is based on S-N curves under constant amplitude loading, the estimation of equivalent stress is done on every random waves. The equivalent stress wasat first estimated by Miner's rule and then by the proposed model which was based on Hashin-Rotem's comulative damage theory regarding nonlinear fatigue cumulative damage behavior. The fatigue lives were predicted from each equivalent stress evaluated. And each predicted fatigue llife was compared with experimental results. The number of cycles of random loads were counted by mean-cross counting method. The reuslts showed that the fatigue life predicted by proposed model was correlated well with the experimental results in comparison with Miner's model.

• 대한산업공학회지
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• 제7권1호
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• pp.33-36
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• 1981

An equipment is subject to shocks which occur randomly according to a Poisson process. The equipment fails when the total cumulative damage reaches a certain prescribed level. An optimal preventive replacement policy is presented when the level of cumulative damage cannot be checked. Renewal theory is used to obtain the results and a case example is presented.

• 대한기계학회논문집
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• 제19권8호
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• pp.1915-1926
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• 1995

The Fatigue characteristics of 8-harness satin woven CFRP composites with a circular hole are experimentally investigated under constant amplitude tension-tension loading. It is found in this study that the fatigue damage accumulation behavior is very random and history-independent, and the fatigue cumulative damage is linearly related with the mean number of cycles to a specified damage state. From these results, it is known that the fatigue characteristics of CFRP composites satisfy the basic assumptions of Markov chain theory and the parameter of Markov chain model can be determined only by mean and variance of fatigue lives. The predicted distribution of the fatigue cumulative damage using Markov chain model shows a good agreement with the test results. For the fatigue life distribution, Markov chain model makes similar accuracy to 2-parameter Weibull distribution function.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 추계학술대회 논문집
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• pp.903-907
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• 1996

Under two level block loading, the carbornitrizing specimen can be expected to show different behavior from other uniform material because the properties of surface layer and inner material are different from each other. In this research, the modified Marco-Starkey cumulative theory, which considers load interaction effect, can predict the life of SCM415 carbornitrizing and original notched and smooth specimen, In the low-high test of carbornitrizing specimen which has long life, however, we may additionally consider the increase of life by means of the stress hardening of inner original material.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2005년도 제17회 워크샵 및 추계학술대회
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• pp.693-697
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• 2005

This study was performed to develop accelerated life test method of the wind-turbine gearbox using accumulated damage theory that used to model the fatigue of parts that receive variable load. The accumulated damage theory was introduced, and the estimation of life and calculation of accelerated life test time was illustrated. As the actual application example, accelerated life test method of the gearbox was described. Life distribution of the wind-turbine gearbox was supposed to follow Weibull distribution and life test time was calculated under the conditions of average life (MTBF) 140,600 hours and 99% reliability for one test sample According to the accumulated damage theory, because test time can shorten in case increase test load, test time could be reduced by 1.2 years when we put the load 1.2 times of rated load than 0.93 times of rated load that is equivalent load calculated by load spectrum of the wind turbine. This time, acceleration coefficient was 21.3. This accelerated test method was used to develop accelerated test method of gear reducer, gear and bearing as well as the industrial gearbox and it is considered to be applied comprehensively to mechanical parts the fatigue of which is happened by load or pressure etc.

• 한국강구조학회 논문집
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• 제9권1호통권30호
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• pp.95-105
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• 1997

Structures subjected to strong seismic excitation may undergo inelastic deformation cycles. The resulting cumulative fatigue damage process reduces the ability of structures and components to withstand seismic loads. Yet, the present earthquake resistance design methods focus mainly on the maximum displacement ductility, ignoring the effect of the cyclic responses. The damage parameters closely related to the cumulative damage need to be properly reflected on the aseismic design methods. In this study, two cumulative damage assessment methods derived from the plastic fatigue theory are investigated. The one is based on the hysteretic ductility amplitude, and the other is based on the dissipated hysteretic energy. Both methods can consider the maximum ductility and the cyclic behavior of structural response. The validity of two damage methods has been examined for single degree of freedom structures with various natural frequencies against two different earthquake excitations.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 가을 학술발표회 논문집
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• pp.353-358
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• 2002

The purpose of this paper was to estimate the cumulative damage of pavement concrete by split tension fatigue test. The split tension fatigue test of variable amplitude loading were performed in two and three stages. The results of the fatigue test by variable amplitude loading showed that the sums of damage were greater than 1 in the increasing sequence loading tests, and less than 1 in the decreasing sequence loading tests. The remaining life estimated by equivalent damage theory was almost similar to that of experimental results.

• 대한토목학회논문집
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• 제7권1호
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• pp.43-54
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• 1987

본 논문에서는 압축반복하중을 받는 콘크리트의 피로누가손상 특성이 연구되었다. 압축을 받는 무근콘크리트의 원주형 공시체에 대한 기초실험을 통하여, 콘크리트의 누가손상에는 여러 인자들 중에서 반복적으로 작용되는 응력의 수준과 재하순서가 가장 크게 영향을 마친다는 것을 발견하였다. 이를 기초로 2단계 응력수준 조건하에서의 피로실험을 실시하여, 콘크리트의 누가손상특성은 Miner의 선형이론을 따르기 보다는 오히려 비선형의 상관관계를 가지며, 응력의 재하방법에 따라 누가손상의 특성과 콘크리트의 정적강도가 변화됨을 구명하였다. 또한 본 연구를 통하여 2 단계 응력수준하에서 콘크리트의 피로특성과 콘크리트구조의 잔존수명을 예측하는데 사용될 수 있는 실험공식이 도출되었다.

• 대한토목학회논문집
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• 제6권4호
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• pp.79-88
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• 1986

본(本) 논문(論文)에서는 크기가 변(變)하는 변동진폭(變動振幅)의 반복하중이 콘크리트구조물(構造物)에 작용(作用)할 경우 피로파괴를 예측할 수 있는 비선형누적손상이론(非線型累積損傷理論)을 제안(提案)하였다. 이를 위하여 콘크리트보에 대한 피로실험이 수행되었으며, 피로하중은 2단계 및 3단계로 크기가 증가하는 경우와 감소하는 경우가 모두 고려되었다. 본(本) 연구(硏究)의 실험결과(實驗結果) 변동진폭(變動振幅)의 반복하중을 받는 콘크리트에 발생하는 누적손상은 피로하중의 크기와 피로하중의 작용순서에 따라 많은 영향을 받는 것으로 나타났으며, 따라서 Palmgren-Miner의 선형손상이론이 콘크리트의 경우 적합하지 않음을 보여주고 있다. 피로하중이 점진적으로 증가하는 경우 Miner의 손상합(損傷合)은 1 보다 크며, 피로하중이 점진적으로 감소하는 경우 이 손상합은 1 보다 작은 것으로 나타났다. 본(本) 논문(論文)에서 제안(提案)된 비선형(非線型) 누적손상이론(累積損傷理論)을 피로하중의 크기와 작용순서의 영향을 고려할 수 있는 보다 진보(進步)된 손상이론으로서, 콘크리트 구조용의 피로해석 및 설계에 있어 하나의 토대가 될 것으로 사료된다.