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박경동(Keyoung-Dong Park),유형주(Hyoung-Ju Ryu) 한국기계가공학회 2006 한국기계가공학회 춘추계학술대회 논문집 Vol.2006 No.-
The security of stability for fracture of all sorts of parts and structure has become a first subject in this days. We have need to organize fatigue characteristics of weldment because fatigue break out suddenly without a change of shape. In this study, we execute the fatigue test according to changes the welding method and weldment at the same materials. It was investigated about fatigue limit according to welding methods of SMAW, FCAW and SAW and to weldment of CASE 1, 2, 3 at the normal temperature and frequency 10㎐. The important results of the experimental study on fatigue characteristics of weld are as follows: The fatigue limit of welding methods was low in the order of SMAW, FCAW, SAW. The fatigue limit of weldment of materials that CASE 1 was determined to the low than CASE 2, CASE 3. The CASE 2 putting the interval of the 2mm creates back plate and make fatigue limit to high.
박경동(Keyoung-dong Park),류찬욱(Chan-uk Ryu) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.10
In this study, CT specimens were prepared from spring steel(SUP9) processed shot peening which was room temperature and low temperature experiment. And we got the following characteristics from fatigue crack growth test carried out in the environment of room temperature and low temperature at 25℃, -30℃, -50℃, -70℃ -100℃ and -150℃ in the range of stress ratio of 0.05 by means of opening mode displacement. The threshold stress intensity factor range △Kth 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 decreased in proportion to descend temperature. It assumed that the fatigue resistance characteristics and fracture strength at low temperature and high temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region.
박경동(KEYOUNG-DONG PARK),박상오(SANG-OH PARK) 한국해양공학회 2002 韓國海洋工學會誌 Vol.16 No.5
In this study, CT specimens were prepared from spring steel(SUP9) which was used in suspension of automobile for room temperature and low temperature survice. We got the following characteristics from fatigue crack growth test carried out in the environment of room temperature and low temperature at 25℃, -30℃, -50℃, -70℃ and -100℃ in the range of stress ratio of 0.05 by means of opening mode displacement. The threshold stress intensity factor range ΔKth in the early stage of fatigue crack growth (RegionⅠ) and stress intensity factor range ΔK in the stable of fatigue crack growth (RegionⅡ) was decreased in proportion to descend temperature. It is assumed that the fatigue resistance characteristics and fracture strength at low temperature and high temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region.
스프링강의 피로크랙 진전거동에 미치는 압축잔류응력의 영향
박경동(Keyoung-Dong Park),정찬기(Chan-Gi Jung) 한국자동차공학회 2002 한국자동차공학회 Symposium Vol.2002 No.11
In this paper, the effect of the compressive residual stresses which were obtained under the various shot velocities on the fatigue behaviors of a spring steel, were investigated. The examination of CT specimen test were executed with the materials(JISG SUP9) which are beign commonly used for the springs of automotive vehicles. As a result, the optimal shot velocity of shot balls were acquired considering the peak values of the compressive residual stresses on the surface of specimen and effect on the speed of the fatigue crack propagation da/dN in stage Ⅱ and the threshold stress intensity factor range ?? in stage Ⅰ. Also the material constant C and the crack propagation index m in the formula of paris law da/dN=O(??) were suggested in this work to estimate the dependency on the shot velocity.
쇼트피이닝가공 스프링강의 압축잔류응력이 피로균열진전거동에 미치는 영향
박경동(Keyoung-Dong Park),장찬기(Chan-Gi Jung) 한국자동차공학회 2002 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2002 No.5_3
The lightness of components required in automobile and machinery industry is requiring high strength of components. In particular, manufacturing process and new materials development for solving the fatigue fracture problem attendant upon high strength of suspension of automobile arc actively advanced. In this paper, the effect of compressive residual stress of spring steel(JISG SUP-9) by shot-peening on fatigue crack growth characteristics in high temperatures(100℃, 150℃, 180℃) was investigated with considering fracture mechanics. So, we can obtain followings.<br/> (1)Compressive residual stress is decreased in high temperature. that is, with increasing temperature.<br/> (2)The effect of compressive residual stress on fatigue crack growth behavior in high temperature is increased below ΔK=17~19MPa√m<br/> (3)The dependence of temperature and compressive residual stress on the parameters C and m in Paris' law formed the formulas such as equations (3),(4),(5),(6).<br/> (4)It was investigated by SEM that the constraint of compress residual stress for plastic zone of fatigue crack tip was decreased in high temperature as compared with room temperature.
박경동(Keyoung-Dong Park),박상오(Sang-Oh Park) 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 and low temperature experiment. And we got the following characteristics from fatigue crack growth test carried out in the environment of room temperature and low temperature at 25℃, -30℃, -50℃, -70℃ and -100℃ in the range of stress ratio of 0.05 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 low temperature and high temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region.
JISG4081SUP7-DIN50GrV4강의 피로강도에 미치는 쇼트피이닝의 영향
박경동(KEYOUNG-DONG PARK),정찬기(CHAN-GI JUNG) 한국해양공학회 2001 韓國海洋工學會誌 Vol.15 No.4
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 (JISG4081SUP7, 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 on low stress condition, the 1st stage shot peening is not affected by nonmetallic inclusion under metal. 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, 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.
스프링강의 피로크랙 진전거동에 미치는 압축잔류응력의 영향
박경동(Keyoung-Dong Park),정찬기(Chan-Gi Jung) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.3
Nowadays, many components used in machinery industry is required lightness and high strength. Therefore, the effects of compressive residual stress by shot-peening which is method to improve fatigue lift of (JISG SUP-9), which used in suspension of automobile, on fatigue crack growth characteristics was investigated with considering fracture mechanics. So, we can obtain followings. (1) The fatigue crack growth rate on stage Ⅱ is conspicuous with the size of compressive residual stress and is dependent on Paris equation. (2) Although the maximum compressive residual stress is deeply and widely formed from surface, fatigue life does not improve than when maximum compressive residual stress is formed in surface. (3) The threshold stress intensity factor range is increased with increasing compressive residual stress. (4) In fracture surface of fatigue crack growth it is investigated that compressive residual stress remarkably retards fatigue crack growth.