• 한국방사성폐기물학회:학술대회논문집
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• 한국방사성폐기물학회 2019년도 춘계학술논문요약집
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• pp.74-75
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• 2019

• 한국기계가공학회지
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• 제6권1호
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• pp.62-70
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• 2007

The development of new materials that are light-weight, yet high in strength has become vital to the machinery, aircraft and auto industries. However, there are a lot of problems with developing such materials that require expensive tools, and a great deal of time and effort. Therefore, the improvement of fatigue strength and fatigue life are mainly focused on by adopting residual stress. The fatigue crack growth rate of the Shot-peened material was lower than that of the Un-peened material. And in stage I, threshold stress intensity factor of the shot-peen processed material is high in critical parts unlike the Un-peened material. Also, fatigue crack growth exponent and number of cycle of the Shot-peened material was higher than that of the Un-peened material. That is concluded from effect of da/dN. And Fatigue life shows more improvement in the Shot-peened material than in the Un-peened material. And compressive residual stress of surface on the Shot-peen processed operate resistance force of fatigue crack propagation.

• 한국안전학회지
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• 제6권4호
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• pp.81-87
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• 1991

We propose the crack growth rate equation which will model fatigue crack growth rate behavior such that constant stress amplitude fatigue crack growth behavior can be predicted. Constant stress amplitude fatigue tests are conducted for four materials under three stress ratios of R＝0.2, R＝0.4 and R＝0.6. Materials which have different mechanical properties i.e. stainless steel, low carbon steel, medium carbon steel and aluminum alloy are used. Through constant stress amplitude fatigue test by using unloading elastic compliance method, it is confirmed that crack closure is a close relationship with fatigue crack propagation. We describe simply fatigue crack propagation behavior as a function of the effective stress intensity factor range ($\Delta$ $K_{eff}$＝U .$\Delta$K) for all three regions (threshold region, stable region). The fatigue crack growth rate equation is given by da / dN＝A($\Delta$ $K_{eff}$­$\Delta$ $K_{o}$ )$^{m}$ / ($\Delta$ $K_{eff}$­$\Delta$K) Where, A and m are material constants, and $\Delta$ $K_{o}$ is stress intensity factor range at low $\Delta$K region. $K_{cf}$ is critical fatigue stress intensity factor.actor.

• Journal of Advanced Marine Engineering and Technology
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• 제31권4호
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• pp.385-393
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• 2007

The strength evaluation of the most weakest junction part is required for the safety design of all structures. Most of all. in order to enhance the reliability and safety of the welding part. whose use is the highest, it is very important to establish the efficient structure manufacturing technology by studying and investigating the evaluation of fatigue strength in various environments. This study analyzed the relations of da/dN, and th according to the welding methods of SMAW, FCAW, and SAW. In the stage II. the value of stress intensity factor range was the highest in SMAW welding method of stress ration R=0.1, and appeared under the sequence of FCAW and SAW and as the completion section of stress intensity factor was low, threshold stress intensity factor was lowly formed in da/dN - The fatigue life of each welding method is sensitively worked in high stress ratio. judging from the fact that the width of life reduction increases in the high stress ratio zone compared to the width of life reduction in the low stress ratio zone. In the fatigue limit of welding methods before corrosion. the welding of SMAW and FCAW shows the same fatigue limit compared to Base metal, and SAW holds the lowest fatigue limit value.

• Journal of Welding and Joining
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• 제13권2호
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• pp.96-105
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• 1995

본 연구에서는 종래의 미소피로균열 성장속도 해석방법에 대한 수정안을 제시하고 수정 후의 방 법에 의해서 계산한 값들과 S4SC 탄소강에 대한 Nisitani와 Goto의 실험결과를 비교하여 계산한 값과 실험데이터 사이에 양호한 일치가 있음을 보였다. 이미 제시된 피로균열성장속도 식에는 하한계수준과 피로한도를 연관시키는 재료상수와 탄소성 거동에 대한 수정 및 균열닫힘효과를 나타내는 방법이 포함되어 있다. 본 연구에서 행한 수정중의 하나는 기하학적인 상수대신에 퍼만(Forman)의 탄성응력 강도계수 범위식을 이용하는 것이고, 다른 하나는 균열이 성장함에 따라 편심형단면으로 되면서 모멘트에 기인해 발생되는 굽힘효과를 고려하는 것이다. 이 방 법을 수명예측에 사용하면 용접구조물은 물론 기계구조물의 보다 정확한 수명예측이 가능할 것 이다.

• Corrosion Science and Technology
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• 제3권1호
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• pp.14-19
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• 2004

Crack growth rate and threshold stress intensity factor for stress corrosion cracking(SCC), $K_{ISCC}$ were measured for type 403 stainless steel in 3,5% NaCl solution at room temperature and SCC was monitored by electrochemical noise technique during $K_{ISCC}$ testing. In rising load test, pits were formed at the tip of pre-crack for the pre-cracked compact tension specimen unlike in smooth round specimen in which only unstable pits were observed and hence immune to SCC. Micro-cracks were found to initiate from the pits in the former specimen, and initiation of micro-crack as well as macro-crack was detected by electrochemical noise technique in rising load $K_{ISCC}$ tests. Crack growth rate increased with increasing either displacement rate or stress intensity factor at crack initiation and was higher in rising load $K_{ISCC}$ test compared to constant load $K_{ISCC}$ test at given stress intensities.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 추계학술대회 논문집
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• pp.106-111
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• 2003

This study made an experiment On fatigue crack propagation da/dn, stress intensity factor range ${\Delta}K$ respectively in room temperature and in low temperature. And we got the following characteristics from fatigue crack growth test carried Out in the environment of room temperature and law temperature at $25^{\circ}C$, $-60^{\circ}C$, $-80^{\circ}C$, and $-100^{\circ}C$ in the range of stress ratio of 0.3 by means of opening made displacement. The threshold stress intensity factor range ${\Delta}Kth$ in the early stage of fatigue crack growth (Mode I) and stress intensity factor range ${\Delta}K$ in the stable of fatigue crack growth (Made II) was decreased in proportion to descend temperature. It assumed that the fatigue resistance characteristics and fracture strength at law temperature and high temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region.

• 한국해양공학회지
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• 제6권1호
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• pp.131-139
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• 1992

The understanding and appllication of fatigue crack propagation mechanism in variable amplitude loading is very important for life prediction of the air travel structures. Particularly, the retardation and arrest behavior of fatigue crack propagation by single tension overloading is essential to the understanding and appllication of fatigue crack propagation mechanism in variable amplitude loading. Numerous studies of the retardation behavior have been performed, however investigations of the arrest behavior have not been enough yet. As for the arrest behavior, Willenborg had reported that the overload shut-off ratio $[R_{so}=(K_{OL})/K_{max})_{crack arrest}]$ had been the material constant, but recently several investigators have reported that the overload shut-off ratio depends upon the stress ratio. In this study, authors have investigated the effect of stress ratio on the threshold overload shut-off ratio to generate arrest of fatigue crack growth in high tensile aluminum alloy 7075-T735 which have used in material for air travel structures, It has been $-0.4\leqqR\leqq0.4$ till now, the region of stress ratio investigated. The threshold overload shut-off ratio has decreased as stress ratio has increased in overall region of -$-0.4\leqqR\leqq0.4$ and the linearity has been seen in this material. Moreover, the experimental equation between $R_{so}$ and R has been made; The relation has been $R_{so}=-R+2.6$.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2001년도 추계학술대회 논문집
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• pp.264-268
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• 2001

In this study, CT specimens were prepared from spring steel(SUP9) processed shot peening which was room temperature, low temperature and 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 $25^{\circ}C,\; 50^{\circ}C, \;100^{\circ}C,\; 150^{\circ}C,\; and\; 180^{\circ}C$ in the range of stress ratio of 0.05 by means of opening mode displacement. The threshold stress intensity factor range $\DeltaK_{th}$ in the early stage of fatigue crack growth (Region I ) and stress intensity factor range $\Delta$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.

• 한국해양공학회지
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• 제16권5호
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• pp.80-87
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• 2002

In this study, CT specimens were prepared from spring steel(SUP9) which was used in suspension of automobile for room temperature and low temperature service. We got the following characteristics from fatigue crack growth test carried out in the environment of room temperature and low temperature at $25^{\circ}C$, ­3$0^{\circ}C$, ­5$0^{\circ}C$, ­7$0^{\circ}C$ and ­10$0^{\circ}C$ 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 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.