• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.10a
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• pp.138-144
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• 2003

Rencentely, the request for the light weight is more incresed in the area of industrial environment and machinery and consistent effort is needed to accomplish high strength of material for the direction of light weight. we got the following characteristic from crack growth test carried out in the range of stress ration of 0.1, 0.3 and 0.6 by means of opening mode displacement. At the content stress ratio, the threshold stress intensity factor crack range ${\Delta}K_{th}$in the early stage of fatigue crack growth (Region I) and dtress intensity factor range ${\Delta}K$ in the stable of fatigue crack growth (Region II) with an increase in ${\Delta}K$. Fatigue life shows more improvement in the Shot-peened material than in the Un-peening material. And compressive residual stress of surface on the Shot peening processed operate resistance force of fatigue. So we can obtain fallowings. (1) The fatigue crack growth rate on stage II is conspicuous with the size of compressive residual stress and is depend on Paris equation. (2) Although the maxium compressive residual stress is deeply and widely formed from surface, fatigue life does not improve than when maxium compressive residual stress is formed in surface. (3) The threshold stress intensity factor range is increased with increasing compressive residual stress.

• Journal of Ocean Engineering and Technology
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• v.18 no.5
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• pp.43-49
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• 2004

The lightness of components required in the automobile and machine industry necessitates the use of high strength components. In particular, the fatigue failure phenomena, which occurs when using metal, increases the danger to human life and property. Therefore, antifatigue failure technology is an integral part of current industries. Currently, the shot peening is used for removing the defect from the surface of steel, while improving the fatigue strength on surface. Therefore, in this paper, the effect of compressive residual stress of spring steel(JISG SUP-9) by shot-peening on fatigue crack growth characteristics in a stress ratio(R=0.1, R=0.3, R=0.6) was investigated, giving consideration to fracture mechanics. By using the methods mentioned above, following conclusions are drawn: (1) The fatigue crack growth rate(da/dN) of the shot-peening material was lower than that of the un-peening material and in stage I, ΔKth, the threshold stress intensity factor of the shot-peen processed material is high in critical parts, unlike the un-peening material. Also m, fatigue crack growth exponent and number of cycle of the shot-peening material, was higher than that of the un-peening material, as concluded from effect of da/dN. (2) Fatigue life shows more improvement in the shot-peening material than in the un-peening material, and the compressive residual stress of surface on the shot-peen processed operate resistance of fatigue crack propagation.

• Journal of Advanced Marine Engineering and Technology
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• v.21 no.5
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• pp.512-521
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• 1997

This paper deals with an evaluation of the residual stress due to shot peening induced in a car¬burized gear tooth and its application to the fatigue crack propagation problem. The residual stress is estimated based on the assumption that the main cause of residual stress is the volume difference between the case and core due to martensitic transformation in cooling, and the influ¬ence of both the reduction of retained austenite and the strain in the surface layer induced by shot peening are considered. The reliability of the method is examined by comparison with stresses measured by the X-ray diffraction method. The stresses intensity factors are computed by the influence function method and the reduction of the factor due to the residual stress is demonstrat¬ed and discussed based on the fracture mechanics.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.2
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• pp.321-329
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• 1998

To ensure the structural integrity of the autofrettaged thick-walled cylinder subjected to cyclic internal pressure loading, the fatigue crack propagation life of the cylinder was evaluated. Stress intensity factors of the external cracked cylinder due to internal pressure and autofrettage loadings were calculated using the finite element method. The fatigue crack propagation lives of the cylinder based on the fracture mechanics concepts were predicted and compared to the experimental fatigue lives evaluated from the C-shaped simulation specimens. There were good correlations between the predicted and experimental fatigue lives within a factor of 3 for the single and double grooved C-shaped simulation specimens. Predicted fatigue crack propagation lives of the double grooved cylinders were about 1.5-5 times longer than those of the single grooved cylinders depending on the levels of autofrettage.

• Journal of Ocean Engineering and Technology
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• v.4 no.1
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• pp.81-87
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• 1990

Fatigue crack closure levels based on the behavior of residual displacements on crack surfaces, are determined analytically according to the microscopic crack closure mechanisms, i.e., whether the first contact of crack surfaces takes place at the very crack tip or on the surfaces near the tip. The comparative analysis on the two models is carried out empirically by the constant amplitude fatigue tests on 2024-T3 aluminum alloy plate, and it shows that under negative stress ratio, the case of the first contact at crack tip gives better agreement with the experimental results than the other.

• Journal of Ocean Engineering and Technology
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• v.4 no.1
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• pp.87-87
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• 1990

Fatigue crack closure levels based on the behavior of residual displacements on crack surfaces, are determined analytically according to the microscopic crack closure mechanisms, i.e., whether the first contact of crack surfaces takes place at the very crack tip or on the surfaces near the tip. The comparative analysis on the two models is carried out empirically by the constant amplitude fatigue tests on 2024-T3 aluminum alloy plate, and it shows that under negative stress ratio, the case of the first contact at crack tip gives better agreement with the experimental results than the other.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.477-480
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• 2000

It is useful way to make indentations near crack tip in order to increase fatigue life or repair a fatigue crack. In this study, bending fatigue tests were performed to investigate the optimal position of the indentations near crack tip. The results shows that fatigue life of the specimen is dramatically increased by indentation and the most effective location is the back of the crack tip.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.2 no.4
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• pp.67-72
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• 2003

In this study, to investigate the effects of 2-step shot peening at the surface of spring steel, crack growth tests are conducted on spring steel and shot peened specimens. And then the residual stresses and fractographs are examined. The crack growth equation that can describe the whole crack growth behavior is used to evaluate the experiment results. The results show that fatigue crack glows slowly in the shot peened specimen than in the unpeened. And in the case of the 2-step shot peened specimen the initial stress intensity factor range and the fracture toughness is higher than the unpeened specimen due to the compressive residual stress. Fractographs show that the compressive residual stress of the surface suppress the fatigue crack opening and consequently slow crack growth rates.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.12
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• pp.3227-3235
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• 1994

This paper deals with an evaluation of the residual stress due to shot peening induced in a carburized gear tooth and its application to the fatigue crack propagation problem. A practical method is proposed on the basis of the assumption that the residual stress is caused by the difference of volume expansion in the case and the core, and the influence of both the reduction of retained austenite and the strain due to shot peening are considered. The evaluated residual stress is close to the measured stress, though the surface stress is rather overestimated. The stress intensity factor is computed by the influence function method, and it is shown that the factor is decreased by the residual stress in shot peened gear tooth. The shot peening is fairly effective to the reduction of fatigue crack growth rate. The crack propagation is simulated and the resistance due to shot peening is quantitatively demonstrated and discussed.

• Journal of Ocean Engineering and Technology
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• v.18 no.6 s.61
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• pp.91-95
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• 2004

In this study, to investigate the effects of shot peening on crack growth behavior, crack growth tests are conducted on spring steels and shot peened cracks. The probabilistic crack growth equation, which can represemt the sigmoidal crack growth behavior as recently reported by Kim and Shim, is used to evaluate the experimental results. The results show that fatigue cracks grows slower in the shot peened specimen than in the unpeened and, due to the compressive residual stress occurring on the specimen surface. In the case of the shot peened specimen, the initial stress intensity factor range and the fracture toughness is higher than the non-peened specimen because the compressive residual stress affects crack growth and fracture of the specimen.