• Journal of the KSME
• /
• v.22 no.1
• /
• pp.40-52
• /
• 1982

복합재료의 개발.실용과 더불어 야기되는 문제중에서, 특히 복합재료가 기계나 구조물에 사용될 경우에는 가장 긴요한 문제는 역시 강도, 특히 파괴와 관련된 강도문제가 되겠다. 균질재료의 파괴거동(취성파괴, 피로파괴, 환경파괴등)을 탄성학적으로 파헤치고, 또한, 나아가서는 파괴를 미연에 예방하는 탄성설계에의 적용에 이르기까지 체계화된 파괴역학을 복합재료의 파괴거동해 석이나 강도설계에 적용시켜 보자는 시도는 일찍부터 이루어져 왔었으나, 탄성적인 이질재료가 결합하는 데서 오는 수학적인 해석사이 난점으로 말미암아 파괴역학적 해석의 기초가 되는 능 력확대계수 K의 해석에서 아직까지는 답보상태에 머물고 있는 것이 현실이다. 여기에서는 복합 재료의 파괴에 파괴역학을 적용시킴에 있어서의 기초적인 사항들을 논하고, 지금까지의 이러한 방향의 연구예들을 정리해 보면서 파괴역학적인 복합재료파괴문제연구에 참고로 삼을가 한다.

• The Korean Journal of Applied Statistics
• /
• v.12 no.2
• /
• pp.621-631
• /
• 1999

재료의 피로 파괴과정은 균열의 발생과 전파 및 성장의 과정을 거쳐 마침내 결정적 균열의 크기가 일정한도를 넘어서면 재료의 파괴가 일어난다. 이 때까지의 시간, 즉 피로 수명이 역정규분포를 따를 때 재료의 수명과 스트레스 수준과 관계를 나타 내는 S-N곡선에 대한 대수선형모형(log-linear model)을 제시하고, 이 모형하에서 피로수명시험에 대한 통계적 최적시험설계방법을 찾는다. 통계적 최적여부에 대한 판단기준으로 설계 스트레스 수준하의 특정 시점에서의 신뢰도에 대한 최우추정량의 점근분산을 최소화하는 방법을 사용하였다.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.10 no.6
• /
• pp.205-212
• /
• 2006

In recent investigations, reinforced concrete beams strengthened with Carbon Fiber Sheets (CFS) subjected to fatigue loading were reported to be failed at the ends of CFS by its debonding. U-shaped CFS were attached to both ends of the CFS when fatigue tests on strengthened beams were conducted to delay and/or prevent fatigue failures of adhesive interface. The experimental parameters of this study were the usage of anchorage at the ends of CFS, the number of CFS layers, and the applied load levels of 60%~90% of the static ultimate load obtained from the static tests. The failure modes and the load cycle-deflection relations were observed and discussed from the experimental results. Those results also showed that the U-shaped anchoring system changes the fatigue failure modes and influences greatly on the fatigue capacity of the strengthened beams.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.15 no.1
• /
• pp.49-60
• /
• 1991

Fatigue behavior of carbon fiber reinforced polyimide composite materials was studied experimentally and analytically. The physical variables, such as cyclic displacements and hysteresis loop energy were observed during fatigue tests. Fatigue life of the investigated [0/90]$_{2S}$ laminates was predicted by H'||'&'||'H models which was proposed based on the fatigue modulus and resultant strain. The predicted fatigue life by H'||'&'||'H curves was reasonably close to the experimental data. Fractography study shows that fatigue failure mechanism of [0/90]$_{2S}$ laminated composite materials involves failure break, matrix tearing and fiber-matrix debonding as well as delamination of layers.

• 한국방재학회:학술대회논문집
• /
• 2010.02a
• /
• pp.79.2-79.2
• /
• 2010

실제 교량 바닥판의 거동은 반복하중에 의한 피로누적 손상에 의해 발생되므로 성능분석을 위해서는 피로 실험결과를 통한 구조거동 분석이 이루어져야 할 것이다. 이에 본 논문에서는 현재 개발 중인 초간편 강합성 바닥판의 피로성능을 파악하기 위해 일점 재하 방식으로 반복 하중을 재하 하였다. 실험체의 거동을 파악하기 위해 변위계를 설치하여 변위를 측정하였고 이 실험의 결과로 신형식 바닥판인 초간편 강합성 바닥판의 피로 파괴 양상을 알 수 있었으며 피로 곡선을 얻을 수 있었다. 하지만 바닥판의 파괴요인 중 외부 환경적 요인과 실제 차량 하중 이동을 모사한 윤하중 재하 시 피로 성능에 대한 연구가 추가로 이루어져야 할 것으로 판단된다.

• Journal of the korean Society of Automotive Engineers
• /
• v.12 no.5
• /
• pp.2-9
• /
• 1990

여기서 논의될 사항들은 피로설계과정과 설계를 위한 최신 피로해석의 기초 및 철합금의 피로제어에 대한 것들이다.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.39 no.10
• /
• pp.952-958
• /
• 2011

On-board IR calibration device has been developed for calibration of spaceborne image sensor. It is composed of a blackbody to provide two different radiance temperatures, tilt mirror with a function of stow and deploy to view the blackbody during the calibration and on-board calibration control unit to control the function of the blackbody and tilt mirror. In this paper, to guarantee the structural safety of the unit, the structural and thermal analysis including a thermo-elastic analysis for verifying structural safety on the soldered part of chips have been performed. In addition, safety margin of the chips on the PCB obtained from the conventional analytical method has been compared to the results from the FEM analysis.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.38 no.4
• /
• pp.437-442
• /
• 2014

The equipment or with a constant torque and a variable stress due to axial vibration such as the turbine-generator system in nuclear power plant show the fatigue fracture behavior. Thus this study whoul aim to measure the torsional stress and analyze the fatigue fracture behavior. To achieve this, we manufactured the equipment similar with turbine-generator system and applied various torsional vibration stress due to external load. In particular, the evaluation was conducted with the existing evaluation methods of the fatigue behavior of known stress-life, strain-life, crack growth assessment methods. With increasing the external load and independent methods tends to decrease the fatigue life was confirmed up to 10 times in 5 kV external load compared to without external load.

• Composites Research
• /
• v.19 no.4
• /
• pp.1-6
• /
• 2006

The effects of aging on fatigue of PSF/AS4 laminates tvas studied using the new energy release rate analysis. The analysis by the variational mechanics has been useful in providing fracture mechanics interpretation of matrix microcracking in cross-ply laminates. This paper describes the changes of the critical energy release rate ${\Delta}Gmc$(microcracking toughness) about the variation of the aging period during fatigue loading. The master plot by modified Pans-law gives a characterization of a material system's resistance to microcrack formation. PSF/AS4 $[0/902]_s$ laminates were aged at four different temperatures based on the glass transition temperature for 60 days. At all temperatures, the toughness decreased with aging time. The decrease of the toughness at higher temperature was faster than at lower temperature. To assess the effects of aging on fatigue, the unaged laminates were compared with the laminates which were aged for 60 days at $170^{\circ}C$ near $180^{\circ}C\;T_g$. The slope of dD/dN versus A 6u, of the aged laminates was lower than that of the unaged laminates. There was a significant shift of the aged data to formation of microcracks at the lower values of ${\Delta}G_m$.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.4 no.3
• /
• pp.19-25
• /
• 1984

In the welded structure, the most dengerous section is welded parts and almost fractures of welded structure occur from welded parts. Accordingly, in other to prevents of fracture, it is important seeking the fracture behavior of welded parts. In this study as basic investigation of fracture behavior of welded parts, it is investigated that local distribution of fracture toughness and effect of multipass electrode welding, also effect of release of residual stress were investigated, as the subjected. material, the used steel having fatigue history and unused steel were selected. As the result of this study, it is dear that the base metal of unused steel and heat affected zone and weld metal are different each other in fracture toughness, and it seems clear that the weld metal may will become source of fracture because of it having the most low fracture toughness. Especially, in the case of crack occur in the used steel, it will be the most brittle section in the structure because of it having low fracture toughness then weld metal. It affirmation that, if welded parts has not flaw, the multi pass electrode welding effective to improve of fracture toughness, also release of residual stress is none effective to improve of fracture toughness in this study.