• Journal of Korean Society of Steel Construction
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• v.10 no.1 s.34
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• pp.85-99
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• 1998

This paper describes an experimental study to examine collapse causes of the lifting cable due to brittle failure of an fitting anchor under the lifting works. Also, in this study an collapse mechanism that was obtained from stress analysis was compared with an actual collapse procedure. Fractographical analysis as well as chemical component test, tension test and Charpy V-Notch impact test for the fractured steel members were carried out. And then, its results were compared with that of normal steel members. Circumferential surface flaws were developed at internal facets of the fitting anchor before tensile stress occurred. Hence, a higher stress than nominal stress was occurred at flaws by stress concentration at the crack tip. Also, stress intensity factor of members increased by crack size of the potential flaws. Because the stress intensity factor at the crack tip was greater than critical values(fracture toughness), brittle fracture occurred under the lifting works. It is judged that the main collapse of the lifting cable is due to brittle fracture of the fitting anchor.

• Proceeding of EDISON Challenge
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• 2013.04a
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• pp.403-408
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• 2013

본 논문은 EDISON_CFD를 이용하여 관상동맥 분지관에서 점도에 따른 유체의 유동현상에 관하여 연구를 하였다. 뉴턴유체인 물의 점성계수 일때와 비뉴턴유체인 혈액의 Carreau model에서의 영전단율 점성계수(${\eta}_0$)와 무한전단율 점성계수(${\eta}_{\infty}$)일 때의 유동현상을 살펴보았다. 그 결과 점도가 증가할수록 재순환 영역에서 유체의 속도가 감소하였고 CF 및 CP값이 감소하는 구간의 수가 증가하여 벽면의 저전단응력으로 인해 생기는 재순환영역의 수가 증가하는 것으로 나타났다.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.1
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• pp.85-93
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• 2012

In this study, the geometry of the weld is used to develop the process of fatigue life prediction. For the development of fatigue life prediction process, bending fatigue test of muffler is conducted to obtain M(Moment)-N(Fatigue life) diagram. Modeling the geometry of the weld which is failed is performed to conduct static load analysis and analysis results are used to calculate the stress concentration factor. The stress concentration factor is used to get the fatigue notch factor and this was based on the fatigue life prediction. As a result of the comparison of test values and predicted values, predicted values are verified.

• International Journal of Highway Engineering
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• v.9 no.1 s.31
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• pp.47-56
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• 2007

Resilient characteristics on unbound pavement materials have been adopted for design and nonlinear analysis of pavement structure under traffic loadings. However, relatively few studies have been done on the nonlinear resilient behavior of unbound materials in Korea. In addition to that, only the limited information is available for estimating the resilient modulus values on subgrade soils. In this study, a laboratory resilient-deformation test under repeated loadings is performed in order to establish the nonlinear characteristics of unbound subgrade soils in test roads. Then, a constitutive model that correlates the resilient modulus with moisture and stress state from field condition is proposed respectively. The results from all procedures are presented in this paper. Finally, a comparative analysis is conducted to identify the proper models in the stress dependent modulus and seasonal moisture condition of subgrade soils in test roads respectively.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.4
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• pp.336-345
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• 2012

In crack growth life, uncertainties are caused by variance of geometry, applied loads and material properties. Therefore, the reliability estimation for these uncertainties is required to keep the robustness of calculated life. The stress intensity factors are the most important variable in crack growth life calculation, but its equation is hard to know for complex geometry, therefore they are processed by the finite element analysis which takes long time. In this paper, the response surface is considered to increase efficiency of the reliability analysis for crack growth life of a turbine wheel. The approximation model of the stress intensity factors is obtained by the regression analysis for FEA data and the response surface of crack growth life is generated for selected factors. The reliability analysis is operated by the Monte Carlo Simulation for the response surface. The results indicate that the response surface could reduce computations that need for reliability analysis for the turbine wheel, which is hard to derive stress intensity factor equation, successfully.

• Journal of the Korean Society for Precision Engineering
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• v.4 no.1
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• pp.27-32
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• 1987

제2장에서 선형타성체에 대한 파괴역학의 일반적인 개념을 약술하였다. 즉 응력확대계수(K) 와 응력집중계수($1_{4}$)의 차이, 에너지 해방율(1$\sub$y)및 $_{4}$와 K의 관계를 이론적으로 살펴보았다. 물론 식(2-35) 및 (2-36) 등은 균열전파 경로가 직선이 아닌 경우에 적용한다는 것은 무리가 있으나 전체적인 이해를 돕기위해서 앞에서와 같이 기술하였다. 세가지 경우의 응력확대 계수 $_{4}$, $_{4}$및 $_{4}$는 하중과 균열의 크기 및 시편의 크기 또는 균열이나 결함을 포함 하고 있는 기계요소 및 구조물의 기하학적인 형상에 관련이 되어져서 결정이 된다.

• Journal of the Korean Society for Precision Engineering
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• v.9 no.2
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• pp.108-115
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• 1992

이종재료의 접합면에 수직으로 존재하는 크랙에 대하여 경계요소 해석을 수행하여, 그 결과 실용가능한 수치 근사해을 얻을 수 있었다. 크랙을 정확히 모델링하기 위하여 크랙표면을 분리영역으로 하는 영역분할법을 채택하였으며, 해의 정확성을 향상시키기 위하여 등매개 2차요소로의 경계분할과 함께 크랙선단에서 표면력의 특이성을 나타내도록 하였다. 응력확대계수는 크랙표면상 절점의 상대변위를 이용하여 결정하였다. 또한 이종 재료내 크랙에 대하여 응력확대계수를 간단히 구할 수 있는 간편해석법을 제안하고 이의 적용 가능한 범위를 제 시하였다.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.36 no.2
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• pp.147-154
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• 2000

실온 대기 중에서 탄소강배관(STS370)의 피로시험을 행하였다. 배관에는 외부결함을 인공적으로 상정하여, 피로균열진전 및 관통의 거동, 균열형상, 누설 및 파단수명, 균열개구변위를 실험과 이론의 양면으로부터 비교·검토하였다. 특히, 배관의 벽두께 관통후에 있어서의 응력확대계수를 평가하기 위하여 새로운 식을 제안하였다. 피로균열이 관벽을 관통하기 전에 있어서는 판모델에 의한 Newman-Raju의 응력확대계수 평가식을 이용하므로서 aspect비와 누설수명 등 관통전의 피로균열성장거동을 평가할 수 있음을 나타내었다. 또한, 피로균열이 관벽을 관통한 후에 있어서는 본 논문에서 제안한 배관모델에 의한 응력확대계수의 평가식을 이용하여 관통후의 균열형상, 파단수명 및 균열개구변위 등 관통후의 피로균열성장거동을 평가하였다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.1
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• pp.36-43
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• 1987

Stress intensity factors are computed by the boundary element method employing the multiregion technique along with the double-point concept. To demonstrate the validity of the current method, the stress intensity factors of the well-known simple models such as a slanted edge crack and an arcular crack are determined, in advanced, which are proved to be in good agreement within 5% with the pre-existing solutions. Z-shaped cracks are analyzed with various branch crack lengths and branching angles.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.130-137
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• 1990

Thermal shock stress intensity factor for an edge-cracked plate subjected to thermal shock is obtained from Bueckner's weight function method. It is shown that thermal shock stress intensity factor has maximum values with variation of time and crack length and that there is most dangerous crack length. By comparing thermal shock stress intensity factor with fracture toughness, the fracture time and critical temperature difference due to thermal shock are determined theoretically. Under constant thermal shock temperature difference, and increase of crack length is shown to increase fracture time. The theoretical fracture time is compared with experimental value measured by acoustic emission method with soda lime glass.