• 수산해양기술연구
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• 제34권1호
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• pp.30-36
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• 1998

Recently, with rapid increase of gas demand, there occurs much interest their security of safety in the gas storage tanks and pressure vessels etc. In order to solve the problems, the occurrence of corrosion fatigue crack and the propagation behavior must be investigated. Especially the occurrence of corrosion fatigue crack and the propagation behavior in the part which has concentrated stress or defects, must be studied more carefully. In this paper, the high-tensile steel of SPV 50 which is much used for building the LPG storage tanks was tested by the use of a plane bending corrosion fatigue tester under the various marine environments and in the air. These experiments were done to investigate the corrosion fatigue crack propagation behavior, the variation of aspect ratio for part through crack and electro-chemical characteristics of the metal. The main results obtained are as follows ; 1. Comparing the same surface crack length with the crack depth, the crack depth toward the thickness of specimen in air propagated faster than that in corrosion environment. 2. The aspect variation of the half elliptical crack can be estimated as following equation; b/a=i-jb/t where a : surface crack length, b : crack depth, t : specimen thickness, i,j : experimental constants but the slope j is decreased as specific resistance decreases. 3. As the specific resistance of corrosion environment decrease or the corrosion fatigue crack propagates, the corrosion potential become less noble.

• 한국자동차공학회논문집
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• 제9권6호
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• pp.135-142
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• 2001

The effect of tensile hold time on the creep-fatigue interaction in AISI 316 stainless steel was investigated. To study the fatigue characteristics of the material, strain controlled low cycle fatigue(LCF) tests were carried out under the continuous triangular waveshape with three different total strain ranges of 1.0%, 1.5% and 2.0%. To study the creep-fatigue interaction, 5min., 10min., and 30min. of tensile hold times were applied to the continuous triangular waveshape with the same three total strain ranges. The creep-fatigue life was found to be the longest when the 5min. tensile hold time was applied and was the shortest when the 30min. tensile hold time was applied. The cause fur the shortest creep-fatigue life under the 30min. tensile hold time is believed to be the effect of the increased creep damage per cycle as the hold time increases. The creep-fatigue life prediction using artificial neural network(ANN) showed closer prediction values to the experimental values than by the modified Coffin-Manson method.

• 대한기계학회논문집A
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• 제20권4호
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• pp.1241-1250
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• 1996

The characteristics of fatigue cumulative damage and fatigue life of 8-harness satin woven CFRP composites with a circular hole under constant amplitude and 2-level block loading are estimated by Stochastic Makov chain model. It is found in this study that the fatigue damage accumulation behavior is very random and the fatigue damage is accumulated as two regions under constant amplitude fatigue loading. In constant amplitude fatigue loading the predicted mean number of cycles to a specified damage state by Markov chain model shows a good agreement with the test result. The predicted distribution of the fatigue cumulative damage by Markov chain model is similar to the test result. The fatigue life predictions under 2-level block loading by Markov chain model revised are good fitted to the test result more than by 2-parameter Weibull distribution function using percent failure rule.

• 한국항공우주학회지
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• 제31권7호
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• pp.63-68
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• 2003

쇼트피닝 가공은 금속부품의 피로특성 향상을 위해 대부분 널리 이용되고 있는 방법이다. 쇼트피닝 가공에 있어 재현성이 있고 신뢰할 수 있는 최적화된 피로특성 증가를 위해 가장 중요한 점이 쇼트피닝 변수 조절이다. 본 논문에서는 최적 피닝강도(알멘강도) 조건에 대한 실험적인 연구가 수행되었다. 피로 특성에 관한 최적피닝의 효과를 검토하기 위하여 회전굽힘피로시험법을 채택하였다. 실험 결과 피로강도와 피로수명이 최적피닝 조건에 의해 크게 증가하였으나 언더피닝 및 오버피닝의 경우에는 감소함을 보였다.

• 한국산업보건학회지
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• 제28권4호
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• pp.374-381
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• 2018

Objective: This study was carried out to examine the factors affecting the fatigue and health promotion behavior of hairdressers and their respective levels. The data were collected from 195 hairdressers working in beauty shops in Daegu and Gyeongsangbuk-do Province using self-administered questionnaires over the period from July 1 to July 31. Methods: A multiple regression model was used to study the factors influencing fatigue and health promotion behavior among hairdressers. Results: This study showed a statistically significant difference in perceived fatigue levels and health promotion behavior according to age, family type, education level, work period, work position, and fatigue level in the past one week. In addition, multiple regression showed that statistically significant factors affecting perceived fatigue were education level, work period, and fatigue level in the past one week. Statistically significant factors affecting health promotion behavior were age and fatigue level in the past one week. The level of perceived fatigue among hairdressers tended to be higher than other workers, and their level of practice of health promotion behavior was generally lower. Conclusions: The improvement of the work environment, such as through the distribution of a proper workload considering workers' characteristics and strengthening of exercise programs to reduce the fatigue level and promote health practices among hairdressers is needed.

• 근관절건강학회지
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• 제6권1호
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• pp.51-72
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• 1999

The purpose of this study is to compar self-reported fatigue and fatigue-regulating behaviors of rheumatoid arthritic patients and normal persons. This study collected the data from 75 rheumatoid arthritic patents visited the departments of internal medicine or orthopedics of four general hospitals T-city and K-city by means of direct interview and questionnaires. in this study also collected data from 75 normal persons who had not been exposed to any other disease in T-city and K-city by means of direct interviews anti questionnaires which were conducted by two trained nurses. This experiment was conducted from August 1, 1998 to October 15, 1998. This study used both MAP(Multi-Dimentional Assessment of Fatigue) developed by Belza(1995) to measure fatigue and the measurement developed by Kwon, Young-Eun to investigate fatigue regulating behaviors. The collected materials were analyzed by means of descriptive statistics, t-test, and the ANCOVA according to the SPSS PC+ program. The findings are as follows : 1. There was the statistically significant difference(t =5.07, p=.000), between rheumatoid arthritic patients(32.76 points) and normal persons(25.81 points) in t-test comparison by group about fatigue. A fatigue degree of rheumatoid arthritic patient group was high in five kinds of lower realms such as common fatigue degree, fatigue severity to be experienced, distress due to fatigue, daily fatigue degree, and fatigue timing at the last week by dimension. 2. There was the significant difference in the number of fatigue-regulating behaviors between rheumatoid of fatigue arthritic patients(9.37 times) and normal persons (8.15 times), but there wasn't any significant difference in the efficiency between rheumatoid arthritic patients(2.85 points) and normal persons (2.78 points) This research suggests two kinds of things as follows : 1. It is necessary to develop an educational program for improving efficiency of fatigue-regulating behaviors as well as some nursing arbitration measures for reducing fatigue of rheumatoid arthritic patients. 2. It is necessary for the future studies to continuously grasp characteristics of fatigue by gender variable by selecting more rheumatoid arthritic male patients.

• 대한기계학회논문집A
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• 제29권5호
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• pp.655-662
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• 2005

This paper investigates the improvement of accuracy and fatigue life of the developed counter pressurized microcellular gears of polyacetal. It is shown that the fatigue life and operational characteristics of the counter pressurized microcellular gears are more improved than conventional injection molded plastic gears by the dynamic gear durability test. For the cases of test sea.5. conventional injection molded sea.5(SGea.) and counter pressurized microcellular gears(CGear) are manufactured. Durability test is performed on both conventional lnjection molded gears and counter pressurized microcellular gears. Accuracy variation and operational characteristics on fatigue life, wear and tooth surface temperature of CGear and Scear are compared and represented. Operational characteristics of the proposed counter pressurized microcellular gears show a good result in this research. The durability limit of counter pressurized microcellular gears is also obtained, and represented by a function of unit load as well as by a function off-factor.

• 한국해양공학회지
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• 제17권3호
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• pp.46-51
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• 2003

Acoustic emission (AE) signals, emanated during local failure of aluminum alloys, have been the subject of numerous investigations. It is well known that the characteristics of AE are strongly influenced by the previous thermal and mechanical treatment of the sample. Possible sources of AE during deformation have been suggested as the avalanche motion of dislocations, fracture of brittle particles, and debonding of these particles from the alloy matrix. The goal of the present study is to determine if AE occurring as the result of fatigue crack propagation could be evaluated by the joint time-frequency analysis method, short time Fourier transform (STFT), and Wigner-Ville distribution (WVD). The time-frequency analysis methods can be used to analyze non-stationary AE more effectively than conventional techniques. STFT is more effective than WVD in analyzing AE signals. Noise and frequency characteristics of crack openings and closures could be separated using STFT. The influence of various fatigue parameters on the frequency characteristics of AE signals was investigated.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2005년도 추계학술대회 논문집
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• pp.1083-1088
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• 2005

As the industrial society develops rapidly, the weight reduction and high strength are demanded gradually. In case of the welded joint for the rolling stock which receives the repeat load, the structural failure can occur easily. However, if the shot peening technique is applied, the durability and the fatigue characteristics of the rolling stock will be improved because the hardness increases and the residual stress is induced. In this study, the fatigue characteristics of shot peened welled joints for the rolling stock was investigated. The crack initiation was examined and hardness was also evaluated. the results show that the fatigue characteristics of welded joints was improved.

• 한국강구조학회 논문집
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• 제11권4호통권41호
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• pp.339-350
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• 1999

이 연구에서는 강교량 주부재의 연결에 주로 사용되는 횡방향 맞대기 용접부를 대상으로 입체결함의 일종인 블로우홀을 인위적으로 도입하고 블로우홀의 크기 및 형상에 따른 피로특성을 정량적으로 평가하기 위해서 일련의 실험을 실시하였다. 정적실험결과 블로우홀을 가진 횡방향 맞대기 용접부의 정적강도는 블로우홀의 크기 및 형상에 관계없이 일정한 경향을 나타내었다. 피로실험결과 블로우홀을 가진 횡방향 맞대기 용접부의 피로강도는 용접루트부 내부에 존재하는 블로우홀의 기하학적 형상이나 결함률에 크게 영향을 받으므로 이로부터 결함률과 피로강도 사이의 상관관계를 정량적으로 규명하였다. 또한 피로균열성장속도와 응력확대계수범위 사이의 관계로부터 블로우홀을 가진 횡방향 맞대기 용접부의 피로수명을 정확하게 산정할 수 있었다.