• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.96-102
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• 1990

Cracks found in pressure vessels have been reported to be mostly semi-elliptic surface cracks. The fatigue crack growth behaviour of the surface cracks on pressure vessel materials, SPV 50Q and API 5A-K55, was studied with the consideration of the crack opening character. To determine the crack opening loads for the surface cracks, the displacement/strain were measured at three positions; the center and the side of the surface crack, the back face of the specimen using CMOD gauge and strain gauges. The experimental results showed that the crack opening load levels measured at the side of the surface crack were generally a little higher than those measured at the back face. As for the crack growth rates at the different parts of the surface crack, the experiments also showed that, if .DELTA.K$_{eff}$ is used, the exponent n of the Paris' law obtained were the same for the rear and the side parts of the surface cracks.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.2
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• pp.54-61
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• 1998

This paper examines the crack growth behavior of 7075-T651 aluminum alloy for small tensile overload under high-low block loading condition. The cantilever beam type specimen with a chevron notch is used in this study. The crack growth and closure are investigated by compliance method. The applied initial stress ratios are R=-0.5 R=0.0 and R=0.25 Crack length, effective stress intensity factor range, ratio of effective stress intensity factor range and crack growth rate etc, are inspected with fracture mechanics estimate.

• International Journal of Precision Engineering and Manufacturing
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• v.1 no.1
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• pp.33-41
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• 2000

Fiber reinforced metal laminates(FRMLs) were new type of hybrid materials. FRMLs consist of high strength metals(Al 5052-H34) and laminated fiber with structural adhesive bond. The effect of resin mixture ratios on the fatigue crack propagation behavior and mechanical properties of aramid fiber reinforced aluminum composites was investigated. The epoxy, diglycidylether of bisphenol A(DGEBA), was cured with methylene dianiline(MDA) with or without an accelerator(K-54). Eight kinds of resin mixture ratio were used for the experiment ; five kinds of FRMLs(1)(mixture of epoxy and curing agent) and three kinds of FRMLs(2)mixture of epoxy, curing agent and accelerator). The characteristic of fatigue crack propagation behavior and mechanical properties FRMLs(2) shows more effecting than that of FRMLs(1).

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.12
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• pp.2055-2060
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• 2003

Striation is a typical pattern observed on the fatigue fracture surface and the spacing is known to correspond to a macroscopic fatigue crack growth rate, and many models for the predict in the formation of such striation have been proposed. However, these theories and methods can't be applied under random loading spectrum. In this study, the fatigue tests were carried out on aluminum alloy under random loading spectrum. The fatigue fracture surfaces were observed in the scanning electron microscope (SEM) and great quantities of SEM micrographs were synthesized and saved in computer system. The space and morphology of several large-scale striations, which are expected to from at the relatively greater load range in loading block, were observed. The crack length for each loading blocks was decided in consideration of regularity and repetition of those striations. It is shown that the applicability of fractographic methods on the fatigue fracture surface under random loading spectrum.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.5
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• pp.539-547
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• 1985

The low-cycle fatigue crack growth behavior of SUS 304 Stainless steel was investigated at 650.deg. C by the nonlinear fracture mechanics. Crack Propagation can be separated in to cycle-dependent and time-dependent, the former is correlated with .DELTA. $J_{f}$ , J-intergral range and the latter is correlated with J', modified J integral. Transition from cycle-dependent to time-dependent crack growth was successfully predicted using the .betha. hypothesis, which was proposed by the authors on the basis of an analysis on the interaction of elastic and creep strain. To investigate the reliability of .betha.-hypothesis, experimenting by the change of stress-level, stress rate and frequency, following conclusions were obtained. (1) High temperature fatigue crack propagation was separated into cycle-dependent and time-dependent. (2) Transition of crack propagation was predicted by .DELTA. $J_{c}$/.DELTA.$_{f}$ or .betha. (3) Lower limit in cycle-dependent crack propagation was obtained..

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.136-137
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• 2006

Crack initiation and short crack propagation was studied on the polished notched surfaces of Cr-Mo prealloy sintered steels with 7.35 $g.cm^{-3}$ sintered density. An ultrasonic resonance test system operating in push-pull mode at 20 kHz and R=-1 was used. It showed that crack initiation took place in several places, small cracks growing oriented to the local pore structure rather than to stress orientation. Their growth rate is markedly higher than the corresponding one of long cracks. Finally, several microcracks join to form a dominant crack.

• Journal of the Korean Society of Safety
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• v.11 no.4
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• pp.10-15
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• 1996

In studying the fatigue strength of fillet welded the section of pressure vessel pad, this study was to evaluate the effect of weld toe notch and to compare the results of numerical analysis with the results of fatigue experiments of fillet welded A5l6 grade 60 steel specimens. The fatigue life for the Bead welded specimen was about 1.4 times as much it as the 1Pad welded specimen. Also, The fatigue life for the 2Pad welded specimen was about 1.5 times as much it as the 1Pad welded specimen. In $da/dN-{\Delta}K$ curve, the fatigue crack growth rate for the 1Pad welded specimen appeared higher than that of the 2Pad welded specimen in the same initial region of ${\Delta}K$, had a similar Inclination In the stabled region.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.2
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• pp.258-267
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• 1998

This study reviews the influence function method(IFM) for calculating stress intensity factors (SIFs, K) and modifies it to apply for the estimating the residual fatigue life for the cracked components under complex stress fields. An IFM has been developed to analyze SIFs for surface cracks which are subjectedto nonuniformly distributed stresses. Through elastic superposition, the influence function method properly accounts for redistribution of stress as the crack grows through the component. This influence function is unique to the given geometry and independent of the loading. Some examples have been provided to show the effectiveness of the IFM including the distributions of K in a residual stress field. The significant effect of residual stress upon fatigue crack growth in a welded component has been demonstrated with the IFM.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.04a
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• pp.341-347
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• 2000

To estimate crack growth rate and cycle ratio uniquely, many investigators have developed various kinds of mechanical parameters and theories. But, these have produced local solution space through single parameter. Neural Networks can perform pattern classification using several input and output parameters. Fatigue damage model by neural networks was used to recognize the relation between da/dN N/Nf, and half-value breadth ratio B/BO0, fractal dimension Df and fracture mechanical parameters in 2024-T3 ability to predict both crack growth rate da/dN and cycle ratio N/Nf within engineering estimated mean error (5%).

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.24 no.1
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• pp.44-49
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• 1988

The paper presents the preliminary results of an esperimental study on crack growth under tension-tension fatigue loading. A purpose of the study is to find the effect of the specimen thickness on crack propagation behaviors. The thickness of the low catbon steel specimens the are used in the experiments are 5, 10, 15,20, and 25 mm. the type of specimen considering in the present study is compact tension specimen.Crack growth behaviors are obseved and measured by travelling microscope. From the study, the followings are found; 1. There is a certain specimen thickness that is the shortest farigue life. The fatigue life of 15mm specimen is the shorter then that of any other opecimen 2. The crack initiation of the thick specimen is slower than that of thin specimen. But the crack propagation rate is just the opposite. 3. The range which is the exponent, m of power law(paris) is 1.98-4.59. the thicker the spec-imen is, the higher the value of m is.