• 대한기계학회논문집
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• 제19권2호
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• pp.463-474
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• 1995

Modified Vainshtok weight function method is developed. The thermal shock stress intensity factors for elliptical surface cracks existed in the thin and thick walled cylinders are determined. The present results are compared with previous solutions and shown to be good agreement with them.

• 한국정밀공학회지
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• 제17권9호
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• pp.151-157
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• 2000

Stress intensity factors for the circumferential surface crack of a long composite cylinder under torsion is investigated. The problem is formulated as a singular integral equation of the first kind with a Cauchy type kernel using the integral transform technique. The mode III stress intensity factors at the crack tips are presented when (a) the inner crack tip is away from the interface and (b) the inner crack tip is at the interface.

• 한국전산구조공학회논문집
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• 제15권3호
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• pp.433-440
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• 2002

본 연구에서는 균일한 인장과 굽힘을 받는 반무한 평판내의 분기균열에 대하여 해석하였다. 중첩의 원리를 이용하여 인장과 굽힘을 받는 분기균열에 대하여 응력 및 모멘트 확대계수를 해석하였다. 응력확대계수는 유한요소법과 J 기저 상호매개적분을 이용하여 해석하였고, 모멘트확대계수는 균열선단의 모멘트로부터 모멘트외삽을 이용하여 계산하였다 무차원화된 응력확대계수와 모멘트확대계수에 대한 수치해석 결과는 분기균열 길이와 주균열의 비, 그리고 분기균열각의 함수로 나타내었다.

• Journal of Welding and Joining
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• 제7권1호
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• pp.28-35
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• 1989

The fatigue crack growth behavior in GTA butt welded joints of Al-Alloy 5052-H38 was examined using Single Edge Notched(SEN) specimens. It is well known that welding residual stress has marked influence on fatigue crack growth rate in welded structure. In the general area of fatigue crack growth in the presence of residual stress, it is noted that the correction of stress intensity factor (K) to account for residual stress is important for the determination of both stress intensity factor range(.DELTA.K) and stress ratio(R) during a loading cycle. The crack growth rate(da/dN) in welded joints were correlated with the effective stress intensity factor range(.DELTA.Keff) which was estimated by superposition of the respective stress intensity factors for the residual stress field and for the applied stress. However, redistribution of residual stress occurs during crack growth and its effect is not negligible. In this study, fatigue crack growth characteristics of the welded joints were examined by using superposition of redistributed residual stress and discussed in comparison with the results of the initial welding residual stress superposition.

• 한국정밀공학회지
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• 제20권4호
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• pp.197-203
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• 2003

Accurate stress intensity factor analyses and crack growth rate of surface -cracked components in inhomogeneous materials are needed fur reliable prediction of their fatigue life and fracture strengths. This paper describes an automated stress intensity factor analysis of three-dimensional (3D) cracks in inhomogeneous materials. 3D finite element method (FEM) was used to obtain the stress intensity factor fur subsurface cracks and surface cracks existing in inhomogeneous materials. To examine accuracy and efficiency of the present system, the stress intensity factor for a semi-elliptical surface crack in a plate subjected to uniform tension is calculated, and compared with Raju-Newman's solutions. Then the system is applied to analyze cladding effect of subsurface cracks in inhomogeneous materials. The results were compared with those surface cracks in homogeneous materials. It is clearly demonstrated from these analyses that the stress intensity factors for subsurface cracks are less than those of surface cracks. Also, this system is applied to analyze cladding effect of surface cracks in inhomogeneous materials.

• 대한기계학회논문집A
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• 제24권6호
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• pp.1547-1556
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• 2000

In this paper, an evaluation method of fracture toughness to apply interfacial fracture mechanics was investigated in adhesively bonded double-cantilever beam (DCB) joints. Four types of adhesively bonded DCB joints with an interface crack were prepared for analyses of the stress intensity factors using boundary element method(BEM) and the fracture toughness test. From the results of BEM analysis and fracture toughness experiments, it is found that the stress intensity factor, K1 is a parameter driving the fracture of adhesively bonded joints. Also, the evaluation method of fracture toughness by separated stress intensity factors of mixed mode cracks was proposed and the influences of mode components for its fracture toughness are investigated in adhesively bonded DCB joints.

• Structural Engineering and Mechanics
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• 제20권3호
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• pp.335-346
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• 2005

The T-stress of cracks in elastic sheets is solved by using the fractal finite element method (FFEM). The FFEM, which had been developed to determine the stress intensity factors of cracks, is re-applied to evaluate the T-stress which is one of the important fracture parameters. The FFEM combines an exterior finite element model with a localized inner model near the crack tip. The mesh geometry of the latter is self-similar in radial layers around the tip. The higher order Williams series is used to condense the large numbers of nodal displacements at the inner model near the crack tip to a small set of unknown coefficients. Numerical examples revealed that the present approach is simple and accurate for calculating the T-stresses and the stress intensity factors. Some errors of the T-stress solutions shown in the previous literature are identified and the new solutions for the T-stress calculations are presented.

• 한국안전학회지
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• 제12권4호
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• pp.27-38
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• 1997

The effect of geometry factors on the combined mode stress intensity factor behaviors of a slant crack in a non-uniform thickness material was analysed by 2-dimensional theoretical analysis. The analysis is based on the Laurent's series expansions of complex potentials where the complex coefficients of the series are determined from the compatibility and the equilibrium conditions of the thickness interface and the stress free conditions of the crack surface. In numerical calculations the perturbation technique is employed. The expressions for the crack tip stress intensity factor are given in the form of power series of dimensionless crack length $\lamda$, and the function of crack slant angle $\alpha$ and thickness ratio $\beta$. The results of numerical calculations for each problems are represented as the correction factors F($\lamda$, $\alpha$, $\beta$). The results clearly show the following characteristics : The correction factors of the combined mode stress intensity factors for a non-uniform thickness material can be defined in the form of F($\lamda$, $\alpha$, $\beta$). The stress intensity factor values for a given crack length are decreased with increase of thickness ratio $\beta$.

• 한국해양공학회지
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• 제2권2호
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• pp.96-103
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• 1988

The stress distribution in the vicinity of the crack tip in the fracture mechanics is ordenarily indicated by the stress intensity factor. In the analysis of stress intensity factors, there are many theoretical and experimental methods. The stress analysis in photoelastic technique is usually made by using the difference of the principal stress of isochromatic fringe patterns. In this paper, the teflon molding technique is adopted to make a test specimen with a circular arc-crack, and that upgraded the accuracy of experiment. As the result, the experimental values of the stress intensity factors for the circular disk with a straight crack are coincided with the theoretical values. But, there is quite a difference between this expermental results on the finite plate for circular arc-crack and its theoretical values on the infinite one. Therefore, a boundary condition with regard to the loading condition on finite disk must be considered.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.117-122
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• 2000

In this paper the stress intensity factor under uniform pressure in the arbitrarily-shaped plane crack configuration transformed elliptic crack by Mobius mapping are determined. Using Dyson's formula Boussinesq-Papkovich potentials for mode I deformation are constructed. In the example the stress intensity factors are approximately calculated by least square method.