• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.5
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• pp.1229-1242
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• 1995

The thermal shock stress intensity factors of semi-elliptical surface crack in finite plate and the stress intensity fractors of embedded elliptical crack in turbine rotor is determined by means of Vainshtok weight function method. In case of semi-elliptical surface crack, the solution is compared with previous solution. The stress intensity factor for embedded elliptical crack in turbine rotor loaded by centrifugal and thermal loading is also determined. In this case, the value of stress intensity factor is larger at crack contour near internal radius surface and is almost constant at the crack contour farther from internal radius surface.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.6
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• pp.701-708
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• 2004

This paper discusses applicability of the enhanced reference stress method to estimate J-integral along the semi-elliptical surface crack front. It is found that angular variations of normalized J­integral are strongly dependent on the geometry, loading mode and loading magnitude. As application of the reference stress approach to semi-elliptical surface cracks implies proportional increases in the normalized J-integral, the present results pose a question in applicability of the reference stress approach. However, investigation of the error in the estimated J-integral in the present work suggests that the enhanced reference stress approach, recently proposed by authors, provides an effective engineering tool fur estimating crack driving force along the semi-elliptical surface crack front.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.4
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• pp.160-166
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• 2001

The theoretical analyses for stresses induced in axial direction in the buried pipelines are reviewed. The influences of the axially directed stresses on the surface elliptical crack are studied in detail and thus some engineering technical informations are provided to use reliability assessment of buried pipelines. The change in temperature, the effect of inner pressure and soil friction in the buried pipeline constrained in axial direction are included to determine the axial stresses in the buried pipeline. Furthermore, the stress induced by the pipeline bending are also considered. The stress intensity factors calculated by two models such as a simple plane crack and an elliptical surface crack for a circumferential surface elliptical crack are compared.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.417-420
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• 2000

The theoretical analyses for stresses induced in axial direction in the buried pipelines are reviewed. The influences of the axially directed stresses on the surface elliptical crack are studied in detail and thus some engineering technical informations are provided to use reliability assessment of buried pipelines. The change in temperature, the effect of inner pressure and soil friction in the buried pipeline constrained in axial direction are included to determine the axial stresses in the buried pipeline. Furthermore, the stress induced by the pipeline bending are also considered. The stress intensity factors calculated by two models such as a simple plane crack and an elliptical surface crack for a circumferential surface elliptical crack are compared.

• Journal of Mechanical Science and Technology
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• v.16 no.2
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• pp.182-191
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• 2002

The reliable stress intensity factor analysis is required for fracture mechanics design or safety evaluation of mechanical joints at which cracks often initiate and grow. It has been reported that cracks in mechanical joints usually nucleate as corner cracks at the faying surface of joints and grow as elliptical arc through cracks. In this paper, three dimensional finite element analyses are performed for elliptical arc through cracks in mechanical joints. Thereafter stress intensity factors along elliptical crack front including two surface points are determined by the virtual crack closure technique. Virtual crack closure technique is a method to calculate stress intensity factor using the finite element analysis and can be applied to non-orthogonal mesh. As a result, the effects of clearance on the stress intensity factor are investigated and crack shape are then predicted.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.7
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• pp.1147-1154
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• 2001

One of major problems in analyzing failure mechanism of real components is the accurate measurement of crack size and shape. The DCPD(Direct Current Potential Drop) method has been widely used for the crack measurement of a structure and finite element analysis has been used for the derivation of calibration equations, which relates the potential drop with the crack depth. In this paper, finite element analyses were performed for semi-elliptical surface cracks with various crack shapes(a/c) and crack depths(a/t). As a result, a calibration equation has been derived for the measurement of a semi-elliptical surface crack in wide plates. Analytical results are compared with experimental results to evaluate the validity and the applicability of the derived equation. The proposed method is expected to provide efficient and accurate measurement of a surface crack during crack growth.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.6
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• pp.916-922
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• 1986

This paper presents the preliminary results of an experimental study on surface crack growth under fatigue loadings. The objective of this paper is to assess the effect of the initial crack size on crack propagation behaviors. Transparent PMMA plate speciments with shallow circular arc notch were used. Crack growth behaviors were observed and measured in two directions by travelling microscopes. The fatigue crack initiated at the deepest part on the initial arc shaped notch and then propagated to depth direction as well as spreading gradually along the notch tip. A considerable number of cycles was needed until the depth crack spreaded to the surface notch tip. When the fatigue crack reached the surface notch tip the crack front became an approximate semi-ellipse, primary semi-elliptical crack. Test results suggest that the relationships between fatigue crack growth rate and stress intensity factor range in both directions can be expressed by power law (Paris) and that relationship in width direction depends upon the crack ratios a$_{1}$/b$_{1}$, of the primary semi-elliptical crack. The relationship between the nondimensional crack lengths in both directions can be represented as the formula: (a/t)$^{n}$ =B(2b/W+A) where n and A are constants and B is seems to be depended upon the crack ratio a$_{1}$/b$_{1}$.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.9
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• pp.2843-2853
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• 1996

The multi-point procedure is developed to predict the shape change of a semi-elliptical surface crack during stable fatigue crack growth. 3-D stress intensity factors along a crack front are calculated using the simplified 3-D J-intergral. Crack growth rate coefficient in the Paris law is assumed to be constant along the crack growth. Crack growth rate is set to be the distance between the two parallel tangent lines on the two semi-elliptic crack fronts before and after crack growth.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.2
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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.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.5
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• pp.823-833
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• 2001

In recent years, the subject of remaining life assessment has drawn considerable attention in chemical plants, where various structural components typically operate at high temperature an pressure. Thus a life prediction methodology accounting for high temperature creep fracture is increasingly needed for the components. Critical defects in such structures are generally found in the form of semi-elliptical surface crack, and the analysis of which is consequently an important problem in engineering fracture mechanics. On this background, we first develop an auto mesh generation program for detailed 3-D finite element analyses of axial and circumferential semi-elliptical surface cracks in a piping system. A high temperature creep fracture parameter C-integral is obtained from the finite element analyses of generated 3-D models. Post crack growth module is further appended here to calculate the amount of crack growth. Finally the remaining lives of surface cracked pipes for various analytical parameters are assessed using the developed life assessment program.