• 대한인간공학회지
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• 제23권4호
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• pp.1-8
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• 2004

The objective of this study is to identify the effects of material position and physical fatigue on postural stability. Ten male subjects participated in this study. After bicycling exercises, their centers of pressure (COPs) were measured under four material handling positions and four excercise levels. The measured COPs were then utilized to calculate postural sway length in each experimental condition. Subjects' postural stability was quantified using the sway length. Results showed that the effect of different material handling position was significant on the postural sway length in both the posterior-anterior axis and the medio-lateral axis. Results also showed that the postural sway length was increased as physical fatigue accumulated, significantly in subject's posterior-anterior axis. The results imply that bearing a material on the back or front with both hands appeared to cause least sway length and instability.

• 해양환경안전학회지
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• 제28권4호
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• pp.667-679
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• 2022

선박의 피로 손상 해석에는 운항적인 요소를 고려한 매개 변수들을 포함하고 있다. 이러한 운항적인 변수들 때문에 설계 단계에서 예측하는 피로 손상도와 실제 운항 조건을 고려한 피로 손상도간의 차이가 발생한다. 마찬가지로 피로 해석에서 적재 하중 조건을 고려할 때 실제 컨테이너선은 다양한 적재 상태가 존재하지만 설계 단계에서 대표 하중 조건을 선택하여 피로 손상도를 계산한다. 실제 하중 조건과 설계시 하중 조건을 적용하였을 때 피로 손상 계산 결과의 차이가 예상됨에도 불구하고 컨테이너선의 하중 조건에 따른 피로 손상 기여도에 관한 연구는 거의 이루어지지 않은 실정이다. 본 연구에서는 컨테이너선의 화물 중량 분포를 변화시켰을 때 피로 손상기여도를 분석하고자 하였다. 일반적으로 설계 단계에서 적용하는 하중 조건뿐만 아니라 다양한 하중 조건을 생성하고 유체동역학 계산으로 얻을 수 있는 선체 거더 하중 및 스펙트럴 피로 해석을 수행하여 얻은 피로 손상도를 확인하였다. 그 결과, 컨테이너선에서 화물 중량 분포 변화는 선체 거더 하중을 변화시켰으며 선체 거더 응력에 영향을 주어 피로 손상의 변화를 야기시키는 것을 알 수 있었다.

• 한국철도학회논문집
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• 제5권3호
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• pp.181-186
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• 2002

Aluminum rolling stocks have been developed for six years in Korea and commercial trainsets are being constructed by the carbuilder. Aluminum alloys are sensitive to various imperfections. In this paper, damages and failures of the aluminum carbody taking place during the process of development are investigated and accumulated data are released. Also, remedies for the failures are suggested and design changes are introduced. It is expected that all informations can contribute to construction of reliable and safe aluminum rolling stocks.

• 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.

• Nuclear Engineering and Technology
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• 제38권3호
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• pp.293-300
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• 2006

A liquid metal reactor (LMR) operated at high temperatures is subjected to both cyclic mechanical loading and thermal loading; thus, creep-fatigue is a major concern to be addressed with regard to maintaining structural integrity. The Korea Advanced Liquid Metal Reactor (KALIMER), which has a normal operating temperature of $545^{\circ}C$ and a total service life time of 60 years, is composed of various cylindrical structures, such as the reactor vessel and the reactor baffle. This study focuses on the creepfatigue crack initiation for a cylindrical Y-junction structure made of 316 stainless steel (SS), which is subjected to cyclic axial tensile loading and thermal loading at a high-temperature hold time of $545^{\circ}C$. The evaluation of the considered creep-fatigue crack initiation was carried out utilizing the ${\sigma}_d$ approach of the RCC-MR A16 guide, which is the high-temperature defect assessment procedure. This procedure is based on the total accumulated strain during the service time. To confirm the evaluated result, a high-temperature creep-fatigue structural test was performed. The test model had a circumferential through wall defect at the center of the model. The defect front of the test model was investigated after the $100^{th}$ cycle of the testing by utilizing a metallurgical inspection technique with an optical microscope, after which the test result was compared with the evaluation result. This study shows how creep-fatigue crack initiation for a high-temperature structure can be predicted with conservatism per the RCC-MR A16 guide.

• Journal of Mechanical Science and Technology
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• 제17권1호
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• pp.1-10
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• 2003

This paper summarizes the results of the fatigue test of four composite bridge decks in extreme temperatures (-30$^{\circ}C$ and 50$^{\circ}C$ ). The work was performed as part of a research program to evaluate and install multiple FRP bridge deck systems in Dayton, Ohio. A two-span continuous concrete deck was also built on three steel girders for the benchmark tests. Simulated wheel loads were applied simultaneously at two points by two servo-controlled hydraulic actuators specially designed and fabricated to perform under extreme temperatures. Each deck was initially subjected to one million wheel load cycles at low temperature and another one million cycles at high temperature. The results presented in this paper correspond to the fatigue response of each deck for four million load cycles at low temperature and another four million cycles at high temperature. Thus, the deck was subjected to a total of ten million cycles. Quasi-static load-deflection and load-strain responses were determined at predetermined fatigue cycle levels. Except for the progressive reduction in stiffness, no significant distress was observed in any of the composite deck prototypes during ten million load cycles. The effects of extreme temperatures and accumulated load cycles on the load-deflection and load-strain response of FRP composite and FRP-concrete hybrid bridge decks are discussed based on the experimental results.

• Restorative Dentistry and Endodontics
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• 제37권2호
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• pp.79-83
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• 2012

Objectives: The purpose of this study was to evaluate the relation between intentionally induced internal stress and cyclic fatigue failure of .06 taper ProFile. Materials and Methods: Length 25 mm, .06 taper ProFile (Dentsply Maillefer), and size 20, 25, 30, 35 and 40 were used in this study. To give the internal stress, the rotary NiTi files were put into the .02 taper, Endo-Training-Bloc (Dentsply Maillefer) until auto-stop by torque controlled motor. Rotary NiTi files were grouped by the number of induced internal stress and randomly distributed among one control group and three experimental groups (n = 10, Stress 0 [control], Stress 1, Stress 2 and Stress 3). For cyclic fatigue measurement, time for separation of the rotary NiTi files was recorded. The fractured surfaces were observed by field emission scanning electron microscope (FE-SEM, SU-70, Hitachi). The time for separation was statistically analyzed using two-way ANOVA and post-hoc Scheffe test at 95% level. Results: In .06 taper ProFile size 20, 25, 30, 35 and 40, there were statistically significant difference on time for separation between control group and the other groups (p < 0.05). Conclusion: In the limitation of this study, cyclic fatigue failure of .06 taper ProFile is influenced by internal stress accumulated in the files.

• 한국철도학회논문집
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• 제13권4호
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• pp.447-454
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• 2010

레일 피로 열화손상유형들은 크게 레일표면에서 발생하는 결함들과 레일내부에서 진전되어 발생하는 결함들로 구분되어질 수 있다. 본 연구에서는 국내에서 연간 누적통과톤수가 가장 많은 도시철도의 운행조건을 고려하여 현장측정을 통해 레일표면 요철성장률을 분석하였으며, 연마 후 누적통과톤수에 따른 시험편을 현장에서 발췌하여 현미경을 이용한 조직검사, 화학성분검사, 마이크로 비커스 경도시험을 수행하였다. 시험결과 신품레일의 경우 유효탈탄층 제거를 위해 약 0.3mm의 초기연마를 시행해야하며, 예방연마의 경우 전구간을 일괄적으로 연마할 경우와 특정 구간별로 구분하여 연마할 경우에 대하여 2가지 방안을 제시하여 레일표면에서 발생하는 RCF결함을 예방하거나 제거할 수 있도록 제시하였다.

• 대한토목학회논문집
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• 제5권3호
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• pp.161-175
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• 1985

판항교(鈑桁橋)의 덮개 판(板), 수직보강재(垂直補强材) 및 연결판(連結板) 등의 용접연결부(鎔接連結部)를 포함하는 실물(實物)을 modeling 하여 직접(直接) 피로시험(疲勞試驗)을 행하지 않고서도 계산 program에 의해 S-N 선도(線圖)를 그리는 방안을 정립하여 서울의 수동대교(水東大橋), 제(第) 3 한강교(漢江橋) 및 춘천(春川)의 강촌교(江村橋) 등에 적용해 보았다. 이에 앞서, SS 41, SS 50, SWS 50, SWS 58 등의 구조강(構造鋼)으로서 소재(素材), 균열방향에 평행용정, 균열방향에 직각 용접의 compact tension 시험편을 제작 피로시험을 행하여 계산 program 중의 data로 쓰여질 재료상수(材料常數) c 및 m 값을 구하였다. 이 결과 다음과 같은 결과들을 얻었다. 덮개판(板)의 경우 다른 두 부분보다 피로강도(疲勞强度)가 매우 낮았다. 덮개판(板)의 경우 두께가 커지면 피로강도(疲勞强度)가 상당히 낮아지는 외에는 치수에 그다지 큰 영향을 받지 않으며, c 및 m 값에는 매우 민감한 영향을 받음을 알 수 있었다. c 값 및 m 값이 적어질수록 피로강도(疲勞强度)가 상당히 커지며, m 값이 적어지면 S-N 곡신의 경사가 매우 급해짐을 알 수 있었다. 이와 같은 연구가 계속되어 더 많은 data가 집적(集積)되면 앞으로 설계(設計)될 판항교(鈑桁橋)의 피로설계지침(疲勞設計指針)을 마련하고, 또 기존(旣存) 판항교(鈑桁橋)의 피로(疲勞)에 대한 내용년한(耐用年限)을 추정(推定)할 수 있는 기본(基本) pattern이 제공(提供)할 수 있으리라 사료된다.

• 한국철도학회논문집
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• 제15권2호
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• pp.141-146
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• 2012

차륜과 레일의 반복적인 구름접촉은 레일 표면결함을 유발하고, 레일 표면결함은 충격하중을 유발하여 소음 진동, 레일파단, 궤도파괴로 이어지고 심할 경우 열차사고(탈선)를 발생할 수 있다. 이러한 레일 표면결함을 제어하기 위한 방법으로 레일연마가 시행되고 있다. 본 연구는 KTX차륜과 UIC레일에서 발생하는 최대 접촉압력을 유한요소해석을 통해 산정하였고, 일반레일 및 열처리레일에 대한 구름접촉피로시험을 수행하여 접촉압력 및 반복횟수에 따른 레일표면 경화층 형성 경향을 분석하였으며, 누적통과톤수에 따라 고속철도 레일에서 발생하는 표면 경화층을 제거하여 건전한 레일표면을 유지하기 위해 0.2mm/2천만톤의 적정 레일연마량을 제안하였다.