• Tunnel and Underground Space
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• v.10 no.3
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• pp.447-456
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• 2000

Rock bridge in rock masses can be considered as one of several types of opening-mode fractures, and also it has been known to have a great influence on the stability of structures in rock mass. In the beginning of researching a rock bridge it used to be studied only in characteristics of its behavior, as considering resistance of material itself. However the distribution pattern of rock bridges, which can affect the stability of rock structures, is currently researched with a fracture mechanical approach in numerical studies. For investigating the effect of rock bridges on the development pattern of hydraulic fractures, the author analyzed numerically the stress state transition in rock bridges and their phenomena with a different pattern of the rock bridge distributions. From the numerical studies, a two-crack configuration could be defined to be representative of the most critical conditions for rock bridges, only when cracks are systematic and same in their length and angle. Moreover, coalescence stresses and onset of propagation stresses could be known to increase with decreasing s/L ratio or increasing d/L ratio. The effect of pre-existing crack on hydraulic fracturing was studied also in numerical models. Different to the simple hydraulic fracturing modeling in which the fractures propagated exactly parallel to the maximum remote stress, the hydraulic fractures with pre-existing cracks did not propagate parallel to the maximum remote stress direction. These are representative of the tendency to change the hydraulic fractures direction because of the existence of pre-existing crack. Therefore s/L, d/L ratios will be identical as a function effective on hydraulic fractures propagation, that is, the K$_1$ value increase with decreasing s/L ratio or increasing d/L ratio and its magnification from onset to propagation increases with decreasing s/L ratio. The scanline is a commonly used method to estimate the fracture distribution on outcrops. The data obtained from the scanline method can be applied to the evaluation of stress field in rock mass.

• Magazine of the Korea Concrete Institute
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• v.17 no.3 s.86
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• pp.50-53
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• 2005

• Magazine of the Korea Concrete Institute
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• v.20 no.3
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• pp.62-66
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• 2008

• Magazine of the Korea Concrete Institute
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• v.22 no.1
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• pp.52-58
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• 2010

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.1A
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• pp.39-48
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• 2012

This study deals with numerical determination of stress intensity factors of adhesively patch-repaired plates with cracks at V-shaped or semicircular notches. The p-convergent anisoparametric model are considered and then three-dimensional virtual crack closure technique is presented using formulations of anisoparametric elements. In assumed displacement fields of an element, strain-displacement relations and three-dimensional constitutive equations are derived with three-dimensional hierarchical shape functions expanded from one-dimensional Lobatto functions. Transfinite mapping technique is used to represent a circular boundary. The present model provides accuracy and simplicity in terms of stress concentration factor, stress distribution, the number of degrees of freedom, and non-dimensional stress intensity factor as compared with previous works in literatures. Stress intensity factors obtained by the three-dimensional virtual crack closure technique are estimated with respect to the variation of width of finite plate, radius of notch root, angular inclination of V-shaped notch, and crack length.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.6
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• pp.1289-1298
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• 1994

The new p-version crack model is proposed to estimate the stress intensity factors of the thick cracked plate under flexure. The proposed model is based on high order theory and $C^{\circ}$-plate element including shear deformation. The displacements fields are defined by integrals of Legendre polynomials which can be classified into three groups such as basic mode, side mode and internal mode. The computer implementation allows arbitrary variations of p-level Up to a maximum value of 10. The stress intensity factors are computed by virtual crack extention approach. The effects of ratios of thickness to crack length(h/a), crack length to width(a/W) and boundary conditions are investigated. Very good agreement with the existing solution in the literature are shown for the uncracked plate as well as the cracked plate.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.2
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• pp.11-17
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• 2016

Powder metallurgy nickel based superalloy has been used in a high temperature part of turbine engine for airplane. The fatigue crack growth behavior was investigated using CT specimens for the materials at room temperature(R.T.), $600^{\circ}C$ and $700^{\circ}C$. The direct current potential drop(DCPD) method suggested by ASTM E647 was used to measure the crack length during fatigue crack growth at various stress ratios. The fatigue crack growth rate at R=0.5 was faster than that at R=0.1 for all temperature conditions and increased with the increase of stress ratio and temperature. Fractography was conducted for analysis of fracture mechanism.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.4
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• pp.306-313
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• 2011

The damage tolerance analysis is required to guarantee the structural safety and the reliability for aircraft components. The damage tolerance method, which evaluate the life considering the initial crack, considers a fatigue design model of the aircraft main structure. The fatigue crack growth life should be calculated in damage tolerance analysis and the inspection time to define the replacement cycle. In this paper, the damage tolerance analysis is performed for a turbine wheel which has complex geometry. The equation of the stress intensity factor for complex geometry is hard to know, so that they are usually processed by finite element analysis which takes long time. To solve this problem, the stress intensity factors at specified crack are obtained by the FEA and the crack growth life is evaluated using the surrogate model which is generated by the regression analysis of the FEA data. From the results, the efficiency of the crack growth life calculation and the damage tolerance analysis could be increased by taking the surrogate model.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.3
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• pp.101-110
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• 2005

In Seoul, structural deterioration is severe in the private masonry buildings which have been built since 1906s. But most of these structures remain without any repair works. As a result, the rate of deterioration is getting faster and these dangerous structures may cause hazardous circumstances to the adjacent structures and neighborhood. The purpose of this study is to investigate the actual conditions of wall cracks among the defect types which occur in private masonry buildings and to analyze the correlation between safety grades and wall cracks for offering the fundamental data. Using these date we can establish basic criteria for safety grades of structures and improve the quality of masonry buildings. The result of this study indicate that there are high correlations between safety grades and the width of crack but much less so with the length. Furthermore, with regard to crack patterns, vertical cracks much more negatively effected the safety grades.

• Journal of Ocean Engineering and Technology
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• v.1 no.1
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• pp.104-110
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• 1987

Fatigue tests by axial loading (R = 0.05) were carried out to investigate fatigue crack growth characteristics of small surface cracks in 2 1/4 Cr-1 Mo steel at room temperature by using flat specimens with a small artificial pit. All the data of the fatigue crack growth rate obtained in the present test are determined as a function of the stress intensity factor range about a semi-elliptical crack, so that the application of linear fracture mechanics to the surface fatigue crack growth and to the fatigue crack growth into depth, and all the data obtained from tests were discussed in comparison with the data of Type 304 stainless steel and two type of mild steel under the same test conditions. The obtained results are as follows: 1)When the cycle ratios are same, surface fatigue crack length and its depth are almost same and fall within a narrow scatter band in spite of different stress levels. 2)Relations of the surface fatigue crack growth rate (da/dN) and fatigue crack growth rate into depth (db/dN) to its stress intensity factor range ($\Delta K_{Ia}, \Delta K_{Ib}$) can be plotted as a straight line at log-log diagram without dependence of stress level and coincide with the data of part-through crack in various steels.