• Journal of Welding and Joining
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• v.11 no.2
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• pp.42-52
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• 1993

The corrosion fatigue fracture behaviour of dual phase steel was investigated in 3% NaCl solution at 302MPa and 137MPa. Fatigue test was conducted by cantilever type of self-made rotary bending fatigue testing machine. The fatigue strength increased with increasing the hardness of 2nd phase. Corrosion pit originated at the boundary of the 2nd phase. The size and number of corrosion pits were influenced by the 2nd phase hardness, and pits remained constant in size just after they were transited into cracks. The life of crack initiation was effected by stress level. The shape of relation of .DELTA. K and da/dN has smaller scattering in it in 3% NaCl solution than that in air. The higher the 2nd phase hardness is, the greater the corrosion fatigue life becomes. Corrosion fatigue fracture behaviour was primarily effected by mechanical factor in case of high stress(302MPa), but by electro-chemical reaction in a lower stress(137MPa). As stress level got lower and hardness of the 2nd phase got higher, the roughness of fracture surface increased.

• Journal of Welding and Joining
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• v.11 no.4
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• pp.112-124
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• 1993

It has been reported that fatigue damage sometimes occurred at the stress concentrated and dynamic loaded structural members of bulk carrier. In this paper, studies on fatigue strength of hull structures are reviewed, and the program for evaluating fatigue strength is developed. And the fatigue crack initiation and propagation on the end part of cargo hold frame of bulk carrier were calculated by FEM stress analysis and the fatigue strength evaluation program. These method can be applied not only to the crack initiation life but also to crack propagation life for the hull structural members at the hull design stage and be effective as the guideline to prevent the crack initiation or to estimate the fatigue strength for repairing of the fatigue damaged structures of real ships.

• Journal of the East Asian Society of Dietary Life
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• v.7 no.1
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• pp.1-11
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• 1997

The purpose of this study was to describe the protein nutritional status of female collegians between nonvegetarian diet groups(14) and vegetarian diet groups(19). Daily intake, protein were calculated from food direct measurement. Urea/creatinine, muscle mass, fatique conditions and hematological parameter were calculated. Blood samples were analyzed for total protein, albumin ammonia, urea, uric acid, creatinine, BUN contents. The results obtained are summarized as following : 1) On total dietary intake, especially Fe, vitamin C, niacin intake, vegetarian groups were higher than non vegetarian groups. 2) On composition of EAA(essential amino acids), vegetarians were highter than non vegetarian of leucine contents, but were lower lysine and threonine contents. 3) On urea / creatinine excretion, vegetarians were higher than non begetarians. Muscle mass were non signicant, fatique condition, vegetarians were normal state. 4) Non vegetarians were increased serum albumin total protein, uric acid, ammonia but vegetarians were decreased BUN, ammonia after experimental diet intake. 5) In process of time after meal, non vegetarians were increased serum albumin total protein, BUN, but vegetarians were decreased ammonia.

• 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.

• Journal of the korean Society of Automotive Engineers
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• v.3 no.3
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• pp.30-38
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• 1981

The fatigue characteristics of Si-Mn spring steel (AISI 9260-H, JIS SUP-6) were investigated on several heat treatment conditions. Repeated impact loads of 10kg-cm and 15kg-cm energy were applied with a cam roller drop hammer type impact fatigue testing machine. Specimens were oil-quenched, and tempered at 350.deg. C, 450.deg. C and 500.deg. C, respectively. Results obtained in these experiments are summarized as follows.; 1) The fatigue life of the specimen is decreased as the magnitude of constant impact energy is increased, regardless of heat treatment. 2) Generally, the fatigue life of the specimen is decreased as the tensile strength of the materials is increased. 3) Within the limit of these experiments, the fatigue life showed abrupt decrease at the tempering temperature of about 400.deg. C 4) The fatigue life is increased as the initial value of applied stress intensity factor(K$_{1}$) is decreased. This tendency is apparent for the low tensile strength materials.

• 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.

• Tribology and Lubricants
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• v.13 no.3
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• pp.48-55
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• 1997

The ball bearing with thin-section raceways which is much lighter than other conventional bearings used in most modem passenger cars and small tracks. The important design parameters of this bearing is the groove radius of raceways, the diametral clearance, the free contact angle and so on. The optimal value of these parameters were determined by considering the dynamic load capacity, the contact angle and the calculated fatigue life. The contact angle between a ball and raceways was calculated by considering the local contact deformation and the structural deformation of thin-section raceways which was estimated by FEM. The raceways were made by means of the press-forming process. The fatigue life tester was designed and manufactured. The fatigue life test was executed and the reliability of this bearing was confirmed.

• 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.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.2
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• pp.79-91
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• 1992

This paper develops the compliance approach to the problem of load sharing between a cracked plate and a patch used to bridge the crack. The theory is validated by using calculated stress intensity factors for the patched and unpatched case to reduce experimentally observed growth rates to common base, Calculations are then made on the effect of patch dimension on fatique life technique. The optimum design of the patch considered the life expectancy and fracture strength of the cracked structure can be performed simply by using this technique.

• Journal of Welding and Joining
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• v.13 no.2
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• pp.60-67
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• 1995

The factors affecting on the fatigue strength of spot_welded specimens have been studied. The influence of initial overloads on the fatigue life of spot_welded tensile_shear specimens is investigated by considering fatigue crack initiation and crack propagation. The change of strain range and the influence of initial overload are correlated on the basis ol strain results. The results of this study are as follows. l) The initial absolute strain range decreased with initial overloads increase, and absolute strain range decreased before transformation of waveform of strain, but increased after transformation of waveform of strain. 2) In case of subsequent point of inflection of offset strain, the increment of this strain decreased with initial overload increase. 3) As initial overloads increase, the deformation behavior of spot welded parts is restricted after overloading.