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압력용기용강의 피로균열전파 및 지연거동에 관한 확률통계적 연구
김선진(S.J. Kim),남기우(K.W. Nam),김부안(B.A.Kim) 한국해양공학회 1995 韓國海洋工學會誌 Vol.9 No.1
The purpose of the present study is to investigate the statistical characteristics of m and C in the fatigue crack propagation law, da/dN=C(ΔK)<SUP>m</SUP> and to studies on the randomness of fatigue crack propagation and retardation behavior. Fatigue tests were performed on 32 CT specimens of SPV50 steel under the same one condition. First, the value of m and C were determined for each specimen, and all the data were analyzed statistically. Second, the material's resistance to fatigue crack propagation is modeled as a stochastic process, which varies randomly along the crack path. The statistical analysis of the material resistance is performed with the data obtained by constant load controlled tests. Finally, retardation behavior was examined experimentally by using a CT specimen, and a retardation parameters were analyzed statistically.
음향방출법에 의한 고강도 구조용 내화강의 열화특성에 관한 연구
강창룡,김현수,남기우,김부안 한국열처리공학회 2000 熱處理工學會誌 Vol.13 No.5
Demand for new nondestructive evaluations is growing to detect tensile crack growth behavior to predict long term performance of materials and structure in aggressive environments, especially when they are in non-visible area. Acoustic emission technique is well suited to these problems and has drawn a keen interests because of its dynamic detection ability, extreme sensitivity and location of growing defects. In this study, we investigated the strength of fire resistance steel for frame structure by tensile test after degradation treatment and analysed acoustic emission signals obtained from tensile test with time frequency analysis methods. In the T and TN specimens(under 600℃-10min) consisting of ferrite and pearlite structure, most of acoustic emission events were produced near yield point, mainly due to the dislocation activities during the deformation. However, B specimen under 600℃-10min had a two peak which was attribute to the presence of martensite phase. The first peak is before yield point and the second after yield point. The sources of second acoustic emission peak were the debonding of martensite-martensite interface and the micro-cracking of brittle martensite phase. In 600℃-30min to 700℃-60min, many signals were observed before yield point and were decreased after yield point.