• Journal of the Korean Society for Railway
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• v.12 no.6
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• pp.895-901
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• 2009

Fatigue fracture of the welded joints of bogie frames is one of unsolved problems. To improve the fatigue strength of the welded joints, various techniques have been applied. In this study, we have investigated the effect of shot peening on the fatigue characteristics of SS400 welded specimens. The fatigue lives of four kinds of welded specimens were examined; welded, PWHT, shot peened, and shot peened after PWHT. The results of the fatigue tests show that the fatigue limit of the shot-peened specimens is higher than that of the welded specimens, and the PWHT specimens have a lower fatigue limit than the welded specimens. It was found that shot peening is a very effective method to improve the fatigue strength of SS400 welded joints.

• Journal of Convergence for Information Technology
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• v.9 no.12
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• pp.157-165
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• 2019

Charles Lindbergh has experienced the uncontrolled situation of the aircraft while he was asleep with open eyes during his Atlantic crossing flight around 20 hours after departure from the New York in 1927 because of the fatigue. According to the NTSB(National Transportation Safety Board) reports, about 40 incidents are related fatigue in each year. The sleep loss is the most wanted item for the NTSB and may cause the similar effect as the alcohol does. The fatigue may affect the management of the threats and errors especially during take-off and landing. In this study, threats and errors of major accidents that NTSB analysed fatigue as a causal factor will be identified in order to understand the seriousness of fatigue.

• Proceedings of the KIEE Conference
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• 2009.04a
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• pp.208-210
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• 2009

본 논문에서는 비닐절연코드의 기계적 피로에 의한 소손패턴과 화재위험성에 대하여 실험, 분석하였다. 비닐절연코드는 2중의 절연피복으로 되어 있으며 도체는 여러 가닥의 소손들로 구성되어 있다. 비닐코드는 반복적인 구부림이나 인장등 기계적 피로에 의해 피복 내 도체가 손상을 입게 되며 전기가 흐르고 있는 상태에서 끊어진 소선들이 접촉과 끊어짐을 반복함으로써 아크와 열이 발생하며 이때 발생한 마크와 열에 의해 피복이 탄화되어 결국에는 착화됨을 볼 수 있었다. 이러한 기계적 피로에 의한 국부 발열과 화재 예방을 위한 기술개발이 필요한 것으로 사료된다.

• Science of Emotion and Sensibility
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• v.3 no.1
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• pp.1-6
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• 2000

단조 작업에 의한 정신적 피로도의 평가를 위하여 피험자에게 1자릿수 숫자 3개를 더하는 연산 작업을 수행하게 하였다. 주관적 평가를 통해 단조작업임이 확인된 task를 사용하여 작업 시간이 증가함에 따라 단조감이 증가하도록 실험과정을 설계하고 생리신호를 측정하였다. 측정된 생리신호 중 심전도, 피부온도, 호흡을 분석하였다. 단조 작업을 수행함에 따라 피부온도의 증가 경향이 나타났으며, 심박 변화율의 전력스펙트럽 분석결과 고주파성분의 감소와 Power spectrum balance가 증가하였다. 특히 power spectrum balance와 주관적 평가치의 상관관계가 높게 나타났다. 또한 상관관계가 높은 생리신호를 사용하여 정신피로를 예측한 결과 (R=0.945)가 정신피로를 잘 나타낼 수 있음을 알 수 있었다.

• Journal of Ocean Engineering and Technology
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• v.2 no.1
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• pp.116-124
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• 1988

해양구조물의 원통조인트에 대한 피로 수명 산출이 전통적으로 실험적 방법에만 의존해 왔음은,원통조인트의 구조가 복잡하여 용접부위 균열의 응력확대 계수 계산이 거의 불가능 했든 것이 주 원인이었다. 최근에 유한요소 3차원 모델을 이용한 계산방법이 개발되어 심히 구조적으로 복잡한 표면 균열의 응력확대계수 산출이 용이하게 되었다. 해양 구조물의 원통조인트에 대한 피로 수명 산출법을 개발하기 위한 연속되는 3부작의 제1부로서 본 논문은 X형 원통 조인트 용접주위 표면 균열의 응력확대 계수 거동을 분석하고 있다. 분석결과를 이용하여 응력확대계수를 엄격한 방법에 의해 계산하였다. 계산된 응력확대계수를 구조적인 관점에서 해석하고 있다.

• Journal of Korean Society of Steel Construction
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• v.16 no.6 s.73
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• pp.847-855
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• 2004

The criterion or specification on fatigue design has been generally based on fatigue strength curve derived by tests on specimens with varying thickness (10-30mm). Making the plate thicker, however, also decreases fatigue strength. It has been noted from the test results and the results of the analysis by fracture mechanics that the effect of thickness cannot be bypassed. From the several fatigue strength curves of specimen tests, modification of fatigue strength on plate thickness has been proposed. In this study, fatigue tests on SM520C-TMC were carried out, and the effects of thickness were evaluated. Finally, in consideration of the thickness, the modification of fatigue strength was derived. Comparing the results of this paper with those of previous studies, an outline of the behavior obtained is similar to previous ones, but the rate of decrease is smaller.

• The Journal of the Convergence on Culture Technology
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• v.8 no.6
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• pp.741-747
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• 2022

Fatigue lowers an individual's ability and makes it difficult to perform work. As fatigue accumulates, concentration decreases and thus the possibility of causing a safety accident increases. Awareness of fatigue is subjective, but it is necessary to quantitatively measure the level of fatigue in the actual field. In previous studies, it was proposed to measure the level of fatigue by expert judgment by adding objective indicators such as bio-signal analysis to subjective evaluations such as multidisciplinary fatigue scales. However this method is difficult to evaluate fatigue in real time in daily life. This paper is a study on the fatigue classification model that determines the fatigue level of workers in real time using speech data recorded in the field. Machine learning models such as logistic classification, support vector machine, and random forest are trained using speech data collected in the field. The performance evaluation showed good performance with accuracy of 0.677 to 0.758, of which logistic classification showed the best performance. From the experimental results, it can be seen that it is possible to classify the fatigue level using speech signals.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.6D
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• pp.881-893
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• 2008

The major objective of this study is to investigate the fatigue damage factor evaluation of immovability crossing for railway turnout by the field test and qualitative analysis. From the field test results of the servicing turnout crossing and qualitative analysis with frictional wear which section stiffness decreased, it was evaluated fatigue life of servicing turnout crossing. Most design practices have not taken advantage of the advanced theories in the modern fracture mechanics and finite element analysis due to complexity of analysis as well as the large quantity of vaguely defined parameters in actual designs. This paper considers fatigue problems in turnout crossing using effective analytical and design tools from the field of qualitative constraint reasoning. A set of software modules was developed for fatigue analysis and evaluation, which is easily applicable in engineering practices of designers. The techniques enable the use complex analysis formulations to tackle practical problems with uncertainties, and present the design outcome in two-dimensional design space solution. Appropriate engineering assumptions and judgments in carrying out these procedures, often the most difficult part for practicing engineers, can be partially produced by using qualitative reasoning to define the trends and ranges, interval constraint analysis to derive the controlling parameters, as well as design space to account for practical experience.

• The Journal of the Convergence on Culture Technology
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• v.7 no.2
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• pp.405-410
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• 2021

In this study, a finite element analysis was performed applying a nonlinear material model and fatigue load conditions to evaluate the service life and spring stiffness of the resilient pad for rail fastening system. As a result of the fatigue analysis, the rate of change in spring stiffness compared to the initial condition was about 16%, indicating that fatigue hardening occurred. As for the stress generated in the longitudinal direction of the resilient pad, the difference between the stress generated at the center and the edge was about 10 times or more. In addition, it was analyzed that the equivalent stress of the outer boundary was more than twice as large as that of the central part. Therefore, it was analyzed that the damage and deformation of the resilient pad are the corners of the resilient pad under actual service conditions. The fatigue life diagram of the resilient pad (S-N curve) was derived using the equivalent stress of the resilient pad according to the fatigue cycles. Using the fatigue life diagram of the resilient pad derived in this study, it is considered that it can be used to predict the fatigue life under the relevant conditions by calculating the equivalent stress of the resilient pad under various load conditions.

• Proceedings of the Korean Nuclear Society Conference
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• 2004.10a
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• pp.859-860
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• 2004