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현가용 강의 부식수명에 미치는 1, 2차 쇼트피닝의 영향
박경동(Kyung-Dong Park),최종완(Jong-Wan Choi),기우태(Woo-Tae Ki) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
The compressive residual stress, which is inducing by shot peening process, has the effect of increasing the intrinsic fatigue strength of surface and therefore would be beneficial in reducing the probability of fatigue damage. However, it was not known that the effect of shot peening in corrosion environment. In this study, the influence of shot peening and corrosion condition for corrosion property was investigated on immersed in supply water, 1% NaCl, 1% H₂SO₄. The immersion test was performed with two kind of specimen. The immersion periods was performed 4320hour(180days). Corrosion potential, weight loss were investigated from experimental results. From test results, the effect of shot peening on the corrosion characteristics was evaluated.
압력용기용 강의 응력비에 따른 저온 피로균열 진전특성에 관한 연구
박경동(KYUNG-DONG PARK),하경준(KYUNG-JUN HA),박형동(HEYOUNG-DONG PARK) 한국해양공학회 2001 韓國海洋工學會誌 Vol.15 No.3
In this study, CT specimens were prepared from Pressure Vessel Steel which was used for pressure vessel plates for room and low temperature service. And we got the following characteristics from fatigue crack growth test carried out in the environment of room and low temperature at 25℃, -30℃, -60℃, -80℃, -100℃ and -120℃ and in the range of stress ratio of 0.05 and 03 by means of opening mode displacement. At the constant stress ratio, the threshold stress intensity factor range △K<SUB>th</SUB> in the early stage of fatigue crack growth (Region Ⅰ) and stress intensity factor range △K in the stable of fatigue crack growth (Region Ⅱ) was increased in proportion to descend temperature. It assumed that the fatigue resistance characteristics and fracture strength at low temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region. The straight line slope relation of logarithm da/dN -△K in Region Ⅱ, that is, the fatigue crack growth exponent m increased with descending temperature at the constant stress ratio. It was assumed that the fatigue crack growth rate da/dN is rapid in proportion to descending temperature in Region Ⅱ and the cryogenic-brittleness greatly affect a material with decreasing temperature.
DIN50CrV4-SAE9254강의 피로강도에 미치는 압축잔류응력의 영향
박경동(KYUNG-DONG PARK),정찬기(CHAN-GI JUNG) 한국해양공학회 2001 韓國海洋工學會誌 Vol.15 No.3
Recently the steel parts used at automobiles are required to be used under high stress more than ever before in need of the weight down. To achieve this requirement of a high strength steel, it must be necessary to decrease inclusion content and surface defect as like decarburization, surface roughness etc.. In this study, the surface conditions are measured to know the influence on fatigue properties by two cases of shot peening of two-stage shot peening and single-stage shot peening. And for this study, two kinds of spring steel (SAE 9254, DIN 50CrV4) are used. This study shows the outstanding improvement of fatigue properties at the case of two-stage shot peening in the rotary bending fatigue test and this is assumed to be from (1) on low stress condition, the 1st stage shot peening is not affected by nonmetallic inclusion under metal. (2) it is possible that the 2nd stage shot peening increases the fatigue life and the high stress but that is affected by nonmetallic inclusion under metal. (3) so far beeasily DIN50CrV4 have made high stress. But, results also show fatigue failures originated at inclusion near surface, and this inclusion type is turned out to be a alumina of high hardness.
쇼트피이닝 가공된 스프링강의 피로균열진전에 미치는 고온의 영향
박경동(Kyung-Dong Park),손명군(Myung-Koon Son) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.4
In this study, CT specimens were prepared from spring steel(SUP9) processed shot peening which was room temperature, high temperature experiment. And we got the following characteristics from fatigue crack growth test carried out in the environment of room, and high temperature at 25℃, 100℃, 150℃, and 180℃ in the range of stress ratio of 0.3 by means of opening mode displacement. The threshold stress intensity factor range ΔKth in the early stage of fatigue crack growth (Region Ⅰ) and stress intensity factor range ΔK in the stable of fatigue crack growth (Region Ⅱ) was decreased in proportion to descend temperature. It assumed that the fatigue resistance characteristics and fracture strength at high temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region.
압력용기용 강의 저온 피로크랙 하한계 특성에 관한 연구(Ⅱ)
박경동(KYUNG-DONG PARK),김정호(JUNG-HO KIM),정찬기(CHAN-GI JUNG),하경준(KYUNG-JUN HA) 한국해양공학회 2000 韓國海洋工學會誌 Vol.14 No.3
In this study, CT specimens were prepared from ASTM SA516 Gr. 70 which wasused for pressure vessel plates for room and low temperature service. And we got the following characteristics from fatigue crack growth test carried out in the environment of room and low temperature at 25℃, -60℃, -80℃ and -100℃ and in the range of stress ratio of 0.05, 0.3 by means of opening mode displacement. At the constant stress ratio, the threshold stress intensity factor range △K<SUB>th</SUB> in the early stage of fatigue crack growth (Region Ⅰ) and stress intensity factor range △K in the stable of fatigue crack growth (Region Ⅱ) were increased in proportion to descending temperature. It was assumed that the fatigue resistance characteristics and fracture strength at low temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region. The straight line slope relation of logarithm da/dN -△K in Region Ⅱ, that is, the fatigue crack growth exponent m increased with descending temperature at the constant stress ratio. It was assumed that the fatigue crack growth rate da/dN is rapid in proportion to descending temperature in Region Ⅱ and the cryogenic-brittleness greatly affect a material with decreasing temperature.
압력용기용 A516강의 저온피로크랙전파특성에 관한 연구
박경동(Kyung-Dong Park),노태영(Tae-Young Ro),김영대(Young-Dae Kim),김형자(Hyung-Ja Kim),손재윤(J-Y Son) 한국해양공학회 1999 韓國海洋工學會誌 Vol.13 No.3(Ⅰ)
In this study, CT specimens were prepared from ASTM A5l6 Gr. 65 which was used for pressure vessel plates for moderate and lower temperature service. Fatigue crack growth test was carried out in the environment of low temperature of 10℃, -10℃, -30℃ and -50℃ and in the range of stress ratio of R=0.05 and 0.3 by means of opening mode displacement<br/> Based on these test results, the characteristics from temperature and stress ratio were shown as follows.<br/> 1) As the stress ratio, R increased da/dN and ΔK of 2nd stage gradually decreased. And as R decreased, the effect of temperature became greater and greater.<br/> 2) As the temperature descended, da/dN decreased on a certain ΔK, and ΔK did in a same da/dN. And the stress ratio, R exerted greater influence at the lower temperature.<br/> 3) The fatigue crack growth constant, m increased at 10℃ and -10℃, and decreased at -30℃ and -50℃ following the increment of stress ratio R. And m increased along with the reduction of temperature greatly decreased at -30℃ to come close to two(2).