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안석환(S. H. Ahn),이수식(S. S. Lee),남기우(K. W. Nam) 한국동력기계공학회 2004 한국동력기계공학회 학술대회 논문집 Vol.- No.-
In pipes used at energy plants, those had exposed to various degradations such as fatigue, creep and corrosion etc. in-service periods. Of them, sometimes, the local wall thinning may result from severe erosion-corrosion damage. Therefore, fracture behaviors of pipes with local wall thinning are very important for the integrity of nuclear power plant. However, studies on the effects of local wall thinning on strength and fracture behaviors of piping system are rarely. In this paper, so, the monotonic bending test was performed of full-scale carbon steel pipes with local wall thinning. A monotonic bending load was applied to wall thinned straight pipe specimens by four-point loading at ambient temperature without internal pressure. From the tests, fracture behaviors and plastic collapse strength of locally thinned pipes were manifested systematically. The observed failure modes were divided into four types; ovalization, crack initiation after ovalization, local buckling and crack initiation after local buckling. Also, the strength and the allowable limit of piping system with local wall thinning were evaluated.
안석환(S. H. Ahn),김태일(T. I. Kim),이문용(M. Y. Kim),김동규(D. K. Kim),남기우(K. W. Nam) 한국동력기계공학회 2008 한국동력기계공학회 학술대회 논문집 Vol.2008 No.11
The surface hardening treatment such as high-frequency induction hardening method is widely used to increase fatigue life and to prevent failure of materials by increasing locally the surface hardness. This method, specially, brings an improvement of static strength by the compressive residual stress of surface due to the hardening. In this study, mechanical properties of high-frequency induction hardened SCM440 steel were investigated. These results, also, were compared with those of base metal and Q/T (tempering after quenching) treatment specimen. From test results, we showed that the partially high-frequency induction hardened SCM440 steel were more improved at static strength, surface hardness, fatigue limit and anti-wear than base metal and Q/T treatment specimen. Specially, fatigue limit of the high-frequency induction hardened SCM440 steel increased more about 52% than that of base metal and about 25% than that of Q/T specimen.
균열치유능력을 가지는 Al₂O₃/SiC 세라믹스의 굽힘강도와 Morphology
박성원(S. W. Park),안석환(S. H. Ahn),손창석(C. S. Son),김성광(S. K. Kim),남기우(K. W. Nam) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
Al₂O₃/SiC composite ceramics were sintered to evaluate the bending strength and elastic wave characteristics. The three-point bending test was carried out under room temperature. The elastic wave was detected by fracture wave detector. The crack healing behavior was investigated from 1373 K to 1723 K. The bending strength of Al₂O₃/SiC composite by nanocomposite is higher than that of Al₂O₃ monolithic. Crack-healing behavior depended on an amount of additive powder Y₂O₃. In Al₂O₃/SiC composite ceramics with 3 wt. % Y₂O₃ for additive powder, the bending strength at 1573 K is about 100% increase than that of the smooth specimens. The strength of Al₂O₃/SiC composite ceramics was a little higher than those of Al₂O₃ monolithic. In proposition to an amount of additive, a large amount of Si and O, and little C were detected.