• 대한기계학회논문집A
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• 제24권6호
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• pp.1557-1564
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• 2000

When the half infinite crack in the orthotropic material strip with a large anisotropic ratio(E11>>E22) propagates with constant velocity, dynamic stress component $\sigma$y occurre d along the $\chi$ axis is derived by using the Fourier transformation and Wiener-Hopf technique, and the dynamic stress intensity factor is derived. The dynamic stress intensity factor depends on a crack velocity, mechanical properties and specimen hight. The normalized dynamic stress intensity factors approach the maximum values when normalized time(=Cs/a) is about 2. They have the constant values when the normalized time is greater than or equal to about 2, and decrease with increasing a/h(h: specimen hight, a: crack length) and the normalized crack propagation velocity( = c/Cs, Cs: shear wave velocity, c: crack propagation velocity).

• Structural Engineering and Mechanics
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• 제21권1호
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• pp.67-82
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• 2005

This study analyzes stress intensity factors for a number of periodic edge cracks in a semiinfinite medium subjected to a far field uniform applied load along with a distribution of eigenstrain. The eigenstrain is considered to be distributed arbitrarily over a region of finite depth extending from the free surface. The cracks are represented by a continuous distribution of edge dislocations. Using the complex potential functions of the edge dislocations, a simple as well as effective method is developed to calculate the stress intensity factor for the edge cracks. The method is employed to obtain the numerical results of the stress intensity factor for different distributions of eigenstrain. Moreover, the effect of crack spacing and the intensity of the normalized eigenstress on the stress intensity factor are investigated in details. The results of the present study reveal that the stress intensity factor of the periodic edge cracks is significantly influenced by the magnitude as well as distribution of the eigenstrain within the finite depth. The eigenstrains that induce compressive stresses at and near the free surface of the semi-infinite medium reduce the stress intensity factor that, in turn, contributes to the toughening of the material.

• 한국자동차공학회논문집
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• 제13권6호
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• pp.63-69
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• 2005

For the case that center crack is surrounded by four small cracks which are symmetrically distributed around center crack, the same values of normalized stress intensity factor of center crack according to the position of the tip of small cracks are located on the smooth curve. And the stress intensity factor according to any position of small cracks can be sufficiently obtained from this curve. The plastic zones between distributed cracks are also investigated by changing the positions of nearly small cracks. The occurrence of plastic zone due to the interaction between center crack and small cracks are analyzed by finite element method. The mechanical behavior at the vicinity of crack tips is investigated by plastic areas. The changes of plastic zones according to positions of distributed cracks are drawn schematically. The safety of materials is also analyzed.

• 한국음향학회지
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• 제10권3호
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• pp.13-18
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• 1991

본 연구에서는 취약한 고체의 표면에 존재하는 crack에 탄성표면파를 입사 시켰을 때 발생하는 반사계수를 측정하여 파괴응력을 해석하는 방법을 연구 분석하였다. Crack이 존재하는 취약한 고체에서의 파괴응력은 임계응력확대계수와 정규화된 최대응력확대계수의 함수로써 나타나며, 이 때 정규화된 최대응력확대계수는 탄성표면파의 반사계수를 측정하여 구할 수 있었다. 실험을 위하여 Pyrex glass원판 중앙에 깊이가 0.5mm~0.9mm인 crack을 제작하였고, SAW wedge transducer를 피치캐치(pitch-catch) 모드로 구성하여 반사계수를 측정하고 파괴응력값을 산출하였으며 UTM(Universal Testing Machine)으로 측정한 값과 비교 분석하였다.

• Steel and Composite Structures
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• 제49권3호
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• pp.271-280
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• 2023

In this study, the three-dimensional finite element method is used to analyze the behavior of corner cracks in finite-thickness plates repaired with a composite patch. The normalized stress intensity factor at the crack front is used as fracture criterion. Comparison of stress intensity factor values at the internal and external positions of repaired quarter-elliptical corner crack was done, for three repair techniques. The influence of mechanical and geometrical properties of the adhesive layer and the composite patch on the variation of the stress intensity factor (SIF) at the crack-front was highlighted. The obtained results show that the application of double patch leads to a remarkable reduction of SIF at the crack front, compared to facial and lateral repairs.

• 대한기계학회논문집A
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• 제40권5호
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• pp.513-523
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• 2016

단순보와 외팔보의 U-노치 및 균열에 대한 응력집중계수 및 응력확대계수를 유한요소법 및 광탄성실험에 의해 해석하였다. 해석결과를 사용하여 응력집중계수 및 응력확대계수의 추정 그래프를 얻었다. 노치의 응력집중계수해석을 위하여 무차원 노치 길이 H(시편의 높이)/h=1.1~2, 무차원 틈 간격 r(노치선단의 반경)/h=0.1~0.5로 하였다. 여기서 h=H-c, c=노치길이이다. 해석결과 틈 길이가 증가할수록 그리고 틈 간격이 좁아질수록 응력집중계수는 증가 한다. 응력집중계수는 단순보가 외팔보다 더 크게 나타나나, 실제 일정한 하중과 노치길이 및 틈 간격 하에서 최대 응력값은 단순보보다 외팔보에서 크게 발생함을 알 수 있었다. 균열해석을 위하여 무차원 균열길이 a(균열길이)/H=0.2~0.5로 하였다. 균열의 길이가 증가 할수록 무차원 응력확대계수는 증가한다. 일정한 하중과 일정한 균열길이하에 응력확대계수값은 단순보 보다 외팔보에서 크게 발생함을 알 수 있었다.

• Structural Engineering and Mechanics
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• 제30권3호
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• pp.317-330
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• 2008

Stress intensity factors for a planar crack parallel to a bimaterial interface are considered. The formulation leads to a system of hypersingular integral equations whose unknowns are three modes of crack opening displacements. In the numerical analysis, the unknown displacement discontinuities are approximated by the products of the fundamental density functions and polynomials. The numerical results show that the present method yields smooth variations of stress intensity factors along the crack front accurately. The mixed mode stress intensity factors are indicated in tables and figures with varying the shape of crack, distance from the interface, and elastic constants. It is found that the maximum stress intensity factors normalized by root area are always insensitive to the crack aspect ratio. They are given in a form of formula useful for engineering applications.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.102-107
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• 2001

Interfacial cracks between an isotropic and orthotropic material, subjected to static far field tensile loading are analyzed using the technique of photoelasticity. The fracture parameters are extracted from the full-field isochromatic data and the same are compared with that obtained using boundary collocation method. Dynamic Photoelasticity combined with high-speed digital photography is employed for capturing the isochromatics in the case of propagating interfacial cracks. The normalized stress intensity factors for static crack is greater when $\alpha=90^{\circ}C$ (fibers perpendicular to the interface) than when $\alpha=0^{\circ}C$ (fiber parallel to the interface) and those when $\alpha=90^{\circ}C$ are similar to ones of isotropic material. The dynamic stress intensity factors for interfacial propagating crack are greater when $\alpha=0^{\circ}C$ than $\alpha=90^{\circ}C$. The relationship between complex dynamic stress intensity factor $|K_D|$ and crack speed C is similar to that for isotropic homogeneous materials, the rate of increase of energy release rate G or $|K_D|$ with crack speed is not as drastic as that reported for homogeneous materials.

• 대한기계학회논문집
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• 제17권7호
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• pp.1710-1718
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• 1993

This paper investigates the problem of a crack approaching two circular holes in an orthotropic infinite plate. The stress intensity factors were obtained by using the modified mapping-collocation method. The present results show excellent agreement with existing solutions for a crack approaching two circular holes in an isotropic infinite plate. In the numerical examples, various types of cross-ply laminated composites were considered. To investigate the effect of orthotropy and geometry(d/R and a/(d-R)) on crack tip singularity, stress intensity factors were considered as functions of the normalized crack length. It is expected that the modified mapping-collocation method can be applied to the analysis of various kinds of cracks existing around the stress-concentration region of composite laminate.

• Structural Engineering and Mechanics
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• 제81권5호
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• pp.565-574
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• 2022

The infrastructures such as offshore, bridges, power plant, oil and gas piping and aircraft operate in a harsh environment during their service life. Structural integrity of engineering components used in these industries is paramount for the reliability and economics of operation. Two regression models based on the concept of Gaussian process regression (GPR) and Minimax probability machine regression (MPMR) were developed to predict stress intensity factor range (𝚫K). Both GPR and MPMR are in the frame work of probability distribution. Models were developed by using the fatigue crack growth data in MATLAB by appropriately modifying the tools. Fatigue crack growth experiments were carried out on Eccentrically-loaded Single Edge notch Tension (ESE(T)) specimens made of API 5L X65 Grade steel in inert and corrosive environments (2.0% and 3.5% NaCl). The experiments were carried out under constant amplitude cyclic loading with a stress ratio of 0.1 and 5.0 Hz frequency (inert environment), 0.5 Hz frequency (corrosive environment). Crack growth rate (da/dN) and stress intensity factor range (𝚫K) values were evaluated at incremental values of loading cycle and crack length. About 70 to 75% of the data has been used for training and the remaining for validation of the models. It is observed that the predicted SIF range is in good agreement with the corresponding experimental observations. Further, the performance of the models was assessed with several statistical parameters, namely, Root Mean Square Error (RMSE), Mean Absolute Error (MAE), Coefficient of Efficiency (E), Root Mean Square Error to Observation's Standard Deviation Ratio (RSR), Normalized Mean Bias Error (NMBE), Performance Index (ρ) and Variance Account Factor (VAF).