• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.28 no.2
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• pp.197-207
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• 1992

Fatigue life and penetration behavior were examined analytically by variety of initial front face crack length and initial crack depth. The fatigue crack shape before penetration is almost semielliptical, and the aspect ratio by calculation using the Newman-Raju's formula is smaller than the value obtained by the experiment. It is found that the crack growth behavior on the back surface after penetration is unique and can be divided into three stage a, b and c. By using the K value proposed by the authors, particular crack growth behavior and the change in crack shape can be evaluated quantitatively. It is found that fatigue life and penetration behavior were more dependent on initial front face crack length than initial crack depth.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.28 no.3
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• pp.286-294
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• 1992

In this paper, the corrosion fatigue crack propagation behavior of structure rolled steel (SWS 41C) was investigated by changing the thickness, and this experiment was done by the three point bending corrosion fatigue tester. The main results obtained are as follows: 1) As the thickness of specimen becomes thicker, the corrosion sensitivity to initial stage crack becomes some sensitive, and that the fatigue life becomes more sensitive. 2) The crack growth rate to initial stage crack (da/dN) was retarded as the thickness of specimen becomes thicker. But after initial stage crack, as the thickness of specimen is more thicker, da/dN is more rapid. 3) As the corrosion fatigue crack length grows, the accelerative factor of thick specimen (t=12mm) is more higher than that of thin specimen (t=6mm). 4) As the corrosion fatigue crack length grows, the corroson potential of both thick specimen and thin specimen becomes more less noble potential, however thick specimen (t=12mm) tends to more less noble potential than that of thin specimen(t=6mm).

• Journal of the Korean Society of Safety
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• v.28 no.1
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• pp.12-17
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• 2013

Considering the wind power system and the rotor blades which are composed of much technology, the wind power blade would be the most dangerous part because it revolves at high speed and weighs about dozens of tons, if the accident happens. Therefore, the light weight composite materials have been replacing as substitutional materials. The object of this study is to examine the delamination and damage for CFRP/GFRP hybrid composite that is used for strength improvement of a wind power blade. The influence of the initial crack length and fiber orientation for the interlaminar delamination was exposed for the blade safety. Plain woven CFRP instead of GFRP was inserted into the layer of the box spar for improving the strength and blade life. DCB(Double Cantilever Beam) specimen was used for evaluating fracture toughness and damage evaluation of interlaminar delamination. The material used in the experiment is a commercial material known as CF 3327 EPC in plain woven carbon prepreg(Hankuk Carbon Co.) and UD glass fiber prepreg(Hyundai Fiber Co.). From the results, crack growth rate is not so different according to the variation of the initial crack length. Mode I interlamainar fracture toughness of fiber direction $0^{\circ}$ is higher than that of $45^{\circ}$. Interlaminar fracture has an effect on fiber direction and K decreased with lower value according to increasing initial crack length. Also energy release rate fracture toughness was evaluated because CFRP/GFRP hybrid composite with a different thickness is under the mixed mode loading condition. The interlaminar fracture was almost governed by mode I fracture even though the mixed mode.

• Nuclear Engineering and Technology
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• v.53 no.4
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• pp.1250-1258
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• 2021

In this paper, the mechanical performance of cracked surface-coated Zircaloy cladding, which has different coating materials, coating thicknesses and initial crack lengths, has been investigated. By analyzing the stress field near the crack tip, the safety zone range of initial crack length has been decided. In order to determine whether the crack can propagate along the radial (r) or axial (z) directions, the energy release rate has been calculated. By comparing the energy release rate with fracture toughness of materials, we can divide the initial crack lengths into three zones: safety zone, discussion zone and danger zone. The results show that Cr is suitable coating material for the cladding with a thin coating while Fe-Cr-Al have a better fracture mechanical performance in the cladding with thick coating. The Si-coated and SiC-coated claddings are suitable for reactors with low power fuel elements. Conclusions in this paper can provide reference and guidance for the cladding design of nuclear fuel elements.

• Journal of Ocean Engineering and Technology
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• v.9 no.1
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• pp.83-91
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• 1995

Surface defects in structural members are apt to be origins of fatigue cracks growth, which may cause serious failure of whole structures. Most structure has a part where stress concentrates such as welded joints, corner parts, etc. And then, analysis on crack growth and penetration from these defects, therefore, is one of the most important subjects for the reliability of LBB design. The present paper has performed an experimental and analysis on the fatigue crack propagation by variety in crack length of surface cracked plate with stress concentration part. The crack growth behavior can be explained quantitatively by using Newman-Raju equation and the stress partitioning method proposed by ASME B&P Code Sec. XI. The stress concentration factor $K_t$ has affected on the crack growth. The crack growth after penetration depends upon the initial front side crack length.

• Journal of the Korean Ceramic Society
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• v.34 no.9
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• pp.927-934
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• 1997

Static and cyclic fatigue tests were carried out for alumina specimen to study the statistical analyses (normal, lognormal and Weibull distribution) of fatigue lifetime data and nominal initial crack length data. Fatigue lifetime data followed Weibull distribution better than normal or lognormal distribution, for the shape parameter of the notched specimen was larger than that of the unnotched specimen. The nominal initial crack length data obtained from fatigue lifetime followed the lognormal and Weibull distribution better than normal distribution, for the coefficient of variation of the unnotched specimen was larger than that of the notched specimen, and shape parameter of unnotched specimen was smaller than that of the notched specimen.

• Journal of Korean Society of Steel Construction
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• v.11 no.4 s.41
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• pp.409-416
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• 1999

The fatigue crack growth analysis based on the fracture mechanics is useful to the estimation of the fatigue life on welded structures under cyclic loading. The analysis procedure in fatigue crack growth under uniform axial loading is applicable to bending fatigue problem as well. The intent of the present study is to show the procedure for calculating the fatigue crack propagation lifetimes of deckplates under bending stress and to explain the crack growth rates for the two dimensional crack problems. It is shown that the fatigue crack grows at a decreasing rate and the fatigue life depends on the initial crack length and the crack shape. The numerically predicted crack growth agree with the experimental data.

• Journal of the Korea Concrete Institute
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• v.13 no.2
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• pp.153-160
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• 2001

In this study, the size effect on axial compressive strength for concrete members was experimentally investigated. Experiment of mode I failure, which is one of the two representative compressive failure modes, was carried out by using double cantilever beam specimens. By varying the eccentricity of applied loads with respect to the axis on each cantilever and the initial crack length, the size effect of axial compressive strength of concrete was investigated, and new parameters for the modified size effect law (MSEL) were suggested using least square method (LSM). The test results show that size effect appears for axial compressive strength of cracked specimens. For the eccentricity of loads, the influence of tensile and compressive stress at the crack tip are significant and so that the size effect is present. In other words, if the influence of tensile stress at the crack tip grows up, the size effect of concrete increases. And the effect of initial crack length on axial compressive strength is present, however, the differences with crack length are not apparent because the size of fracture process zone (FPZ) of all specimens in the high-strength concrete is similar regardless of differences of specimen slenderness.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1109-1114
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• 2003

The initial crack often occurs on the bonded interface and it is the general cause of the interface fracture. It is very significant to establish the measurement method of interfacial crack by applying the ultrasonic technology into the interface of bonded dissimilar materials. In this paper, the interfacial crack length was measured by ultrasonic attenuation coefficient in the Al/Epoxy bonded dissimilar materials of double-cantilever beam(DCB). The energy release rate, G, was obtained by the experimental and Ripling's equation measurement of compliance. The experimental results represent that the relation between interfacial crack length for the ultrasonic attenuation coefficient and energy release rate is increased proportionally. From the experimental results, a measurement method of the interfacial crack length by the ultrasonic attenuation coefficient was proposed and discussed.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.5
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• pp.740-745
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• 1987

For the prediction of the crack growth initiation from a blunt notch or a precrack in a prestrained material under plane strain tension and small-scale yielding conditions, a microscopic fracture criterion is proposed in terms of the crack tip opening displacement(COD) needed for the attainment of fracture strain at a microstructural distance. Smooth blunting of a crack tip with an initial root radius is assumed, and strain distributions on the crack-line axis are calculated at each deformation stage until the distributions against an original distance normalized to the COD are insensitive to an initial root radius. This case of no initial-root-radius effect is taken as for a sharp crack tip, on which the criterion is applied to determine the characteristic length of material from a critical COD for a fatigue-precracked specimen. The predicted COD at the fracture initiation from a crack with an initial root radius or a prestraining shows reasonable agreement with experimental values.