• Structural Engineering and Mechanics
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• 제62권2호
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• pp.225-236
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• 2017

The purpose of this work is to predict ductile fracture of structural steel under extremely low cyclic loading experienced in earthquake. A cumulative damage model is proposed on the basis of an existing damage model originally aiming to predict fracture under monotonic loading. The cumulative damage model assumes that damage does not grow when stress triaxiality is below a threshold and fracture occurs when accumulated damage reach unit. The model was implemented in ABAQUS software. The cumulative damage model parameters for steel base metal, weld metal and heat affected zone were calibrated, respectively, through testing and finite element analyses of notched coupon specimens. The damage evolution law in the notched coupon specimens under different loads was compared. Finally, in order to examine the engineering applicability of the proposed model, the fracture performance of beam-column welded joints reported by previous researches was analyzed based on the cumulative damage model. The analysis results show that the cumulative damage model is able to successfully predict the cracking location, fracture process, the crack initiation life, and the total fatigue life of the joints.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.136-141
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• 2004

The gear in various mechanical components easily occurs at damages by the external torque. The main failure modes of the gear are surface pitting with the tooth surface and breakage with tooth root by caused fatigue. Therefore, the gear is very important role in the reliability research since it may cause fatal damage of entire system such as the gear box in automobile transmission. In this study, the failure mode of the gear was analyzed and accelerated durability analysis was employed for the life estimation of spur gears. In the case of assumed load spectrums, the reliability of spur gears was evaluated by inverse power law-Weibull accelerated life test model with cumulative damage exposure.

• Composites Research
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• 제28권4호
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• pp.182-190
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• 2015

The phenomenological evolution laws of damage can be defined either based on residual life or residual strength. The failure of a specimen can be defined immediately after or before fracture. The former is called in this paper by "failure defined by approach I" and the latter "failure defined by approach II." Usually at failure there is a discontinuity of loading variables and, because of this, damage at failure is discontinuous. Therefore the values of damage at failure by two different approaches are not the same. Based on this idea the sequence effects of the phenomenological evolution law of damage given by $dD/dN=g(D)f({\Phi})$ were studied. Thin-walled graphite/epoxy tubes consisting of four of $[{\pm}45]_s$ laminates were used for the experimental study of sequence effects and the effects of mean stress on fatigue life. It was found that the sequence effects in two step uniaxial fatigue for $[{\pm}45]_s$ graphite/epoxy tubular specimen showed that a high-low block loading sequence was less damaging than a low-high one.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.445-450
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• 2003

This study was performed 10 develop the accelerated life test method using Weibull-IPL(Inverse Power Law) model for mechanical components. Weibull-IPL model is concerned with determining the assurance life with confidence level and the accelerated life test time From the relation of weibull distribution factors and confidence limit, the testing times on the no number of failure acceptance criteria arc determined. The mechanical components generally represent wear and fatigue characteristics as a failure mode. IPL based on the cumulative damage theory is applied effectively the mechanical components to reduce the testing time and to achieve the accelerating test conditions. 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% confidence level for one test sample. According to IPL, because test time call be 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.

• 한국기계가공학회지
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• 제14권3호
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• pp.131-140
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• 2015

The purpose of this study is to predict the fatigue life of a planet carrier of a slewing reducer for a tower crane. To predict the fatigue life of the carrier, the inertia endurance test was carried out, and then the input torque profile for the reducer was obtained. The load profile acting on the planet pins that assembled the carrier was calculated from the measured input torque profile using commercial gearbox analysis software. The stress profiles of the carrier weak points were analyzed from the calculated load profile and boundary conditions using commercial FE software, and the stress cycles were determined using the rainflow counting method. Finally, the fatigue life of the carrier was predicted using the equivalent stress range by considering the effect of mean stress, and an S-N curve was drawn up using the GL guideline and the cumulative damage law.

• 한국해안·해양공학회논문집
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• 제27권4호
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• pp.246-257
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• 2015

피해 자료의 부족에 따른 불확실성 뿐만 아니라 시간의 진행에 따른 불확실성을 고려하기 위하여 추계학적 확률과정을 이용하여 시간에 따른 구조물의 피해 경로를 정량적으로 추적하였다. 누적피해도와 내구년수의 분포함수를 시간의 함수로 산정하여 추계학적 확률과정을 적용할 때 주의해야 하는 중요한 특성들을 제시하였다. 특히, 본 연구에서는 추계학적 확률과정을 경사제 피복재에 적용하여 시간에 따른 누적 피해도를 추적할 수 있는 방법을 제안하였다. 확률과정의 매개변수들을 추정하기 위하여 개발된 표본경로기법을 이용하여 경사제 피복재의 시간에 따른 누적 피해도가 포화거동을 따른다는 사실이 확인되었다. 또한 누적 피해도 산정시 중요한 역할을 하는 멱함수의 지수를 정량적으로 산정하여 경사제 피복재의 누적 피해도를 시간에 따라 추적하는 것이 가능했다. 마지막으로 한계수준을 다양하게 변화시키면서 파괴확률의 거동특성을 해석하였다.

• 대한산업공학회지
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• 제19권2호
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• pp.15-21
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• 1993

This paper considers the optimal design of accelerated life test in which the stress is linearly increased. It discusses the special case when the life distribution under constant stress follows an exponential distribution and the accelerated equation satisfies the inverse power law. It is assumed that cumulative damage is linear, that is, the remaining life of test units depends only on the current cumulative fraction failed and current stress(cumulative exposure model). The optimization criterion is the asymptotic variance of the maximum likelihood estimator of the log mean life at a design stress. The optimal increasing rate is obtained to minimize the asymptotic variance. Table of sensitivity analysis is given for the prior estimators of model parameters.

• Structural Engineering and Mechanics
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• 제60권1호
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• pp.71-90
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• 2016

In this paper, the normalized variable V=(log N-B)(log ${\Delta}{\sigma}-C$-C), as derived from the probabilistic S-N field of Castillo and Canteli, is taken as a reference for calculation of damage accumulation and probability of failure using the Miner number in scenarios of variable amplitude loading. Alternative damage measures, such as the classical Miner and logarithmic Miner, are also considered for comparison between theoretical lifetime prediction and experimental data. The suitability of this approach is confirmed for it provides safe lifetime prediction when applied to fatigue data obtained for riveted joints made of a puddle iron original from the Fao bridge, as well as for data from experimental programs published elsewhere carried out for different materials (aluminium and concrete specimens) under distinct variable loading histories.

• 대한교통학회지
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• 제6권2호
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• pp.21-33
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• 1988

부적정한 도로포장 구조물의 설정 및 유지보수의 적정관리 미흡으로 표면의 피해와 소성변형이 장기간 발생된다. 이로 인한 가요성 통제 구조물의 파괴 원인은 일반적으로 포 장재료의 동질성, 선형탄성 상태의 가정 하에서 분석되었다. 그러나 아스팔트 재료의 특성은 엄밀히 분석해서 완전한 선형탄성이라고는 볼 수 없음은 잘 알려져 있다. 따라서 근본적으 로 포장체의 수명과 파양 예측에 오류 발생가능성이 높다 하겠다. 금번 연구는 이와 같은 종전의 경험적인 선형탄성 방법이 아닌 탄성일소성 상태하의 격자(mechano-lattice) 이론이란 새로운 기법을 도입하였다. 특히 마이너(Miner's Law) 이론의 누적손실과 확률을 적용하여 포장체의 피노수명과 손실을 예측할 수 있다. 금번 이론은 실제로 호주 빅토리아주의 멜보른(Melbourne)시 일부 지역구간을 모형으 로 선정되었다. 분석결과 가장 최적화된 도로포장 각층의 두께와 재료 선정을 하기 위하여 일정기간의 교통량, 상대적 손실지수와 잔여응력 및 표면 변위, 대기온도 그리고 습도의 영 향을 종합적으로 고려하여야 한다.

• 항공우주정책ㆍ법학회지
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• 제22권2호
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• pp.27-51
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• 2007

The cumulative result of the work by the ICAO Secretariat, the Secretariat Study Group and the Council Special Group on the Modernization of the Rome Convention of 1952 are two draft Conventions, namely: "Draft Convention on Compensation for Damage Caused by Aircraft to Third Parties, in case of Unlawful Interference", and "Draft Convention on Compensation for Damage Caused by Aircraft to Third Parties" The core provisions of the former draft Convention are as follows: The liability of the operator is strict, that is, without the necessity of proof of fault. It would be liable for damage sustained by third parties on condition only that the damage was caused by an aircraft in flight(Article 3). However, such liability is caped based on the weight of the aircraft(Article 4). It is envisaged to create an independent organization called the Supplementary Compensation Mechanism, with the principle purpose to pay compensation to persons suffering damage in the territory of a State Party, and to provide financial support(Article 8). Compensation shall be paid by the SCM to the extent that the total amount of damages exceeds the Article 4 limits(Article 19). The main issues on the farmer draft Convention are relating to breaking away from Montreal Convention 1999, no limits on individual claims but a global limitation on air carrier liability, insurance coverage, cap of operators' strict liability, and Supplementary Compensation Mechanism. The core provisions of the latter draft Convention are as follows: the liability of the operator is strict, up to a certain threshold tentatively set at 250,000 to 500,000 SDRs. Beyond that, the operator is liable for all damages unless it proves that such damage were not due to its negligence or that the damages were solely due to the negligence of another person(Article 3). The provisions relating to the SCM and compensation thereunder do not operate under this Convention, as the operator is potentially for the full amount of damages caused. The main issues on the latter draft Convention are relating to liability limit of operator, and definition of general risks. In conclusion, we urge ICAO to move forward expeditiously on the draft Convention to establish a third party liability and compensation system that can stand ready to protect both third party victims and the aviation industry before another 9/11-scale event occurs.