• 한국정밀공학회지
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• 제6권3호
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• pp.78-89
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• 1989

Applicability of tearing modulus based on J-integral proposed by Paris et al is investigated using compact tension specimens of strutural alloy steel (SCM4). Both general fracture test and instability fracture test are performed. The applied tearing modulus, ( $T_{j}$)app estimated from the real load vs. crack growth curve measured from experiments are compared with that estimated from the limit load vs. crack growth curve. The results are : (1) the $T_{j}$parameter could be applied to predict crack growth instability : (2) The use of ( $T_{j}$)app estimated from the load vs. crack growth curve, proposed in this study could be well predicted crack growth instability instead of that estimated form the limit load vs. crack growth curve.e.

• 대한기계학회논문집
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• 제13권5호
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• pp.928-937
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• 1989

본 연구에서는 Shih등이 제안한 찢어짐 계수인 Ｔ$_{\delta}$의 불안정 파괴 매개 변수로서의 적용 가능성을 컴팩트 인장 시편(compact tension specimen dlgk CTS로 칭함)을 사용하여 검토한다. 이를 위하여 시험기에 스프링을 부착하여 시편에 불안정 파괴 실험을 수행한다. 재료의 불안정성을 판정하는 찢어짐 계수를 구하기 위해서는 CTOD-정항 곡선을 결정해야 한다. CTOD는 하중선 변위를 측정하여 CTOD- 하중선 변위 관계식으로 평가한다.한다.

• Structural Engineering and Mechanics
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• 제71권1호
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• pp.65-75
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• 2019

In this article, the dynamic fracture instability characteristics, including dynamic crack propagation and crack branching, in PMMA brittle solids under dynamic loading are investigated using the discrete element method (DEM) simulations. The microscopic parameters in DEM are first calibrated using the comparison with the previous experimental results not only in the field of qualitative analysis, but also in the field of quantitative analysis. The calibrating process illustrates that the selected microscopic parameters in DEM are suitable to effectively and accurately simulate dynamic fracture process in PMMA brittle solids subjected to dynamic loads. The typical dynamic fracture behaviors of solids under dynamic loading are then reproduced by DEM. Compared with the previous experimental and numerical results, the present numerical results are in good agreement with the existing ones not only in the field of qualitative analysis, but also in the field of quantitative analysis. Furthermore, effects of dynamic loading magnitude, offset distance of the initial crack and initial crack length on dynamic fracture behaviors are numerically discussed.

• 대한기계학회논문집
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• 제12권1호
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• pp.53-63
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• 1988

본 연구에서는 COA와 COD저항곡선의 기울기가 밀접한 관계가 있다는 점을 고려하여 COD저항곡선을 이용하여 현재까지 거의 연구결과가 없는 Ｔ$_{\delta}$에 의한 불안정균열성장문제를 검토하기로 하고, 이때 필요한 외부하중에 의한 부하 찢어짐계수 Ｔ$_{{\delta}{\app}}$ 의 평가방법에 대해서도 생각해 보기로 한다.한다.

• 한국기계가공학회지
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• 제10권3호
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• pp.79-86
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• 2011

The dynamic instability and natural frequency of elastically restrained pipe conveying fluid with the attached mass and crack are investigated. The pipe system with a crack is modeled by using extended Hamilton's Principle with consideration of bending energy. The crack on the pipe system is represented by a local flexibility matrix and two undamaged beam segments are connected. In this paper, the influence of attached mass, its position and crack on the dynamic stability of a elastically restrained pipe system is presented. Also, the critical flow velocity for the flutter and divergence due to the variation in the position and stiffness of supported spring is studied. Finally, the critical flow velocities and stability maps of the pipe conveying fluid with the attached mass are obtained by the changing parameters.

• 대한기계학회논문집
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• 제17권9호
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• pp.2223-2233
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• 1993

An engineering method is suggested to calculate the applied load versus crack extension in the elastic-plastic fracture. The condition for an increment of crack extension is set by a critical increment of crack-up opening displacement(CTOD). The ratio of the CTOD increment to the incremental crack extention is a critical crack-tip opening angle(CTOA), assumed to be constant for a material of a given thickness. The Dugdale model of crack-tip deformation in an infinite plate is applied to the method, and a complete solution for crack extension and crack instability is obtained. For finite-size specimens of arbitrary geometry in general yielding, an approximate generalization of the Dugdale model is suggested so that the approximation approaches the small-scale yielding solution in a low applied load and the finite-element solution in a large applied load. Maximum load is calculated so that an applied load attains either a limit load on an unbroken ligament or a peak load during crack extension. The proposed method was applied to three-point bend specimens of a carbon steel SM45C in various sizes. Reasonable agreements are found between calculated maximum loads and experimental failure loads. Therefore, the method can be a viable alternative to the J-R curve approach in the elastic-plastic fracture analysis.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.344-347
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• 2007

In this paper, the stability of a cracked cantilever beam subjected to follower force is presented. In addition, an analysis of the flutter instability(flutter critical follower force) of a cracked cantilever beam subjected to a follower compressive load is presented. Based on the Timoshenko beam theory. The vibration analysis on such cracked beam is conducted to identify the critical follower force for flutter instability based on the variation of the first two resonant frequencies of the beam. Besides, the effect of the crack's intensity and location on the flutter follower force is studied. The crack section is represented by a local flexibility matrix connecting two undamaged beam segments. The crack is assumed to be in the first mode of fracture and to be always opened during the vibrations. Generally, the critical follower force for flutter is proportional to the crack depth.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 추계학술대회논문집
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• pp.865-868
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• 2006

In this paper, a dynamic behavior(natural frequency) of a cracked simply supported pipe conveying fluid is presented. In addition, an analysis of the flutter and buckling instability of a cracked pipe conveying fluid due to the coupled mode (modes combined) is presented. Based on the Euler-Bernouli beam theory, the equation of motion can be constructed by using the Lagrange's equation. The crack section is represented by a local flexibility matrix connecting two undamaged beam segments. The stiffness of the spring depends on the crack severity and the geometry of the cracked section. The crack is assumed to be in the first mode of fracture and to be always opened during the vibrations. This study will contribute to the safety test and stability estimation of structures of a cracked pipe conveying fluid.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.328-332
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• 2000

Following the method described in ASTM E1737, J resistance curves are measured for Cr-Mo steel SA387, and Cr steel A240 which are used as piping materials in nuclear industry. Crack driving force diagrams are generated in order to find out instability points in crack growth. The $J_{appl}$ curves, which are used in the crack driving force diagram, are obtained from EPRI J estimation method and the finite element analysis. Crack growth instability points are plotted in load-crack length plane and the results are discussed.

• 한국소음진동공학회논문집
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• 제17권1호
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• pp.10-16
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• 2007

In this paper, the dynamic stability of a cracked simply supported pipe conveying fluid is investigated. In addition, an analysis of the flutter and buckling instability of a cracked pipe conveying fluid due to the coupled mode(modes combined) is presented. Based on the Euler-Bernouli beam theory, the equation of motion can be constructed by using the Galerkin method. The crack section is represented by a local flexibility matrix connecting two undamaged pipe segments. The stiffness of the spring depends on the crack severity and the geometry of the cracked section. The crack is assumed to be in the first mode of fracture and to be always opened during the vibrations. This results of study will contribute to the safety test and a stability estimation of the structures of a cracked pipe conveying fluid.