• Journal of the Society of Naval Architects of Korea
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• v.30 no.4
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• pp.74-82
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• 1993

The present paper deals with the structural safety assessment techniques for independent type B spherical LNG tank against fatique crack initiation and propagation, which contains fellowing 3 steps. 1) Prediction of long term distribution of wave induced stresses and fatique crack intiation life using cumulative damage theory which were described at the 1st report. 2) Surface crack propagation analysis to verify that initial defects cannot penetrate tank plate. 3) Passing-through fatigue crack propagation analysis was performed based on LBF(Leak Before Failure ) theory.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.10a
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• pp.703-708
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• 1997

In this study, the fatigue tests are performed on simply-supported R/C beams strengthened with steel plate and CFS (Carbon fiber sheet). Analysis results by Weibull distribution are compared with the test data. The unknown Weibull distribution parameters are estimated based on observations recorded in fatigue test. Safety factors for the number of cycles and the stress level are obtained. S-N-P curves are also generated from these testes and probabilities of failure.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.672-675
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• 1995

Because of a sudden growth of the research of fatigue failure, recent machines or structures have been designed by damage tolerance design in many fields. Consequently, it is the most primary factor to clarity the specific character of fatique failure in the design of machines or structures considering reliability. A statistical analysis is required to analyze the outcome of an experiment or a life estimate by reason of that fatigue failure contains lots of random elements. Reliability analysis which has tukenn the place of the existing analyses in the consideration of the uncertainty of a material, is a very efficient way. Even reliability analysis, however, is not a perfect way to analyses the uncertainties of all the materials. This thesis would refer to a newly conceived data analysis that the coefficient of a system could cause the ambiguity of the relationship of an input and output.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1998.10a
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• pp.91-99
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• 1998

A correlation between the low-cycle fatigue life and the scuffing-failure life is demonstrated using the plastic strain in boundary lubricated sliding. Loadings proportional to hardness with three different lubricated conditions were used to evaluate the plastic strain. As the results of scuffing tests using vacuum pump oils in nitrogen gas, plastic strain shows 0.0062, and In the mineral oils and commercial engine oils in air, plastic strain show 0.0042 and 0.00092. Those are very useful to describe quantitatively the real lubricated sliding conditions, and are very effective to find the relation between the low-cycle fatigue life and the scuffing life.

• Proceedings of the KSR Conference
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• 2005.11a
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• pp.1083-1088
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• 2005

As the industrial society develops rapidly, the weight reduction and high strength are demanded gradually. In case of the welded joint for the rolling stock which receives the repeat load, the structural failure can occur easily. However, if the shot peening technique is applied, the durability and the fatigue characteristics of the rolling stock will be improved because the hardness increases and the residual stress is induced. In this study, the fatigue characteristics of shot peened welled joints for the rolling stock was investigated. The crack initiation was examined and hardness was also evaluated. the results show that the fatigue characteristics of welded joints was improved.

• Tribology and Lubricants
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• v.13 no.2
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• pp.39-45
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• 1997

The shot peening treatment were conducted for improving the strength of rolling contact fatigue of machine element like a gear. This paper was undertaken to analyze the influence of shot peening treatment for inner race of ball bearing on the rolling contact fatigue. Shot peening treatment were applied to the full hardened and the carbonitrided bearing. And the rolling contact fatigue life test and X-ray diffraction test were carried out. The results of this study showed that the fatigue life of ball bearing in the clean and the contaminated oil could be improved by shot peening treatment. This effect was found to be more pronounced to the full hardened bearing. These facts might be due to the generation of compressive residual stress and the strain hardening of surface layer by shot peening treatment. The failure of the shot peened bearing were presumed to initiate at surface.

• Journal of the Korean Society of Industry Convergence
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• v.24 no.4_2
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• pp.435-441
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• 2021

This research was performed to study the effect of the Ni + Mo addition on the fatigue properties in 12Cr steel. After heat treatment of 12Cr steel and 12Cr-Ni-Mo steel, tensile tests, impact tests, hardness tests, and rotary bending fatigue tests were performed, respectively. The fatigue fracture surface was observed and analyzed using SEM and EDS. The fatigue limit of 12Cr steel was 554 MPa, which was 49 MPa higher than 505 MPa of 12Cr-Ni-Mo steel. Striations, which are the shape of the typical fatigue fracture surface, were observed at the fracture surface near the starting point of fatigue fracture in the 12Cr steel and 12Cr-Ni-Mo steel. However, unlike the case of 12Cr steel, 12Cr-Ni-Mo steel also had a mixed fracture surface with the fatigue and the ductile fracture surface. When brittle non-metallic inclusions exist near the starting point of fatigue failure, the crack propagation was further promoted and the fatigue life was drastically reduced.

• International Journal of Highway Engineering
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• v.11 no.4
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• pp.95-105
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• 2009

This study was conducted to investigate the effects of concrete flexural strength and surface smoothness, which were pay factors of concrete pavements, on pavement performance, and to develop the methodologies to determine the proper allowable ranges according to the magnitudes of those pay factors. The concrete flexural strength was analyzed using the AASHTO, power, and linear fatigue failure models, and the surface smoothness was analyzed for the roughness indices of PSI, IRI, and PrI using the AASHTO model. The analysis results showed that the allowable range of the flexural strength should be determined using the rate between the deficiency and strength, and the penalty should be linearly proportional to the strength deficiency rate because the linear relationship between the strength deficiency rate and the reduction in pavement life was observed. As the initial surface smoothness became better, the smoothness deficiency rate should be larger. The penalty due to the surface smoothness deficiency should also be linearly proportional to the smoothness deficiency rate.