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균열 진전에 의한 Al₂O₃ 복합 세라믹스의 비파괴 평가
김진욱(J.W. Kim),김해숙(H.S. Kim),안석환(S.H. Ahn),손창석(C.S. Son),김종순(J.S. Kim),남기우(K.W. Nam) 한국동력기계공학회 2007 한국동력기계공학회 학술대회 논문집 Vol.- No.-
The elastic waves released by inducing vickers indentation were detected by fracture wave detector. From the result of wavelet analysis of elastic wave signal, the smooth specimen and heat-treated crack healing specimen of 0.3 ㎛ Al₂O₃ monolithic and Al₂O₃/SiC composite ceramics had characteristics of frequency about 58 ㎑. The dominant frequencies increased with increasing the amount of Y₂O₃. It is known that wave frequency of homogeneous materials is converged on around dominant frequency. The dominant frequency has direct connection with the bending strength.
섬유기기용 Al₂O₃계 세라믹스의 균열치유거동과 균열치유재의 강도특성
안병건(B. G. Ahn),김미경(M. K. Kim),김현수(H. S. Kim),안석환(S. H. Ahn),김진욱(J. W. Kim),남기우(K. W. Nam) 한국동력기계공학회 2005 한국동력기계공학회 학술대회 논문집 Vol.- No.-
Alumina ceramic for textile machinery was sintered and subjected to three-point bending. A semicircular surface crack was made on each sample. Crack-healing behavior was systematically studied, as a function of crack-healing temperature, crack size. The bending strength and fracture toughness of the crack-healed sample from 1200℃ to 1400℃ was investigated. A statistical approach based on Weibull distribution was applied to the test data to evaluate the dispersion in the fracture toughness. Alumina ceramic for textile machinery have the ability to heal after cracking, from over 1300℃. The material can completely heal a 65 ㎛ diameter semielliptical crack. The fracture toughness could be explained by 2-parameter Weibull distribution.
Al₂O₃ 복합 세라믹스의 굽힘강도와 Mapping 특성 평가
김해숙(H.S. Kim),안석환(S.H Ahn),손창석(C.S. Son),김종순(J.S. Kim),남기우(K.W Nam) 한국동력기계공학회 2007 한국동력기계공학회 학술대회 논문집 Vol.- No.-
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.
Al₂O₃ 복합 세라믹스의 고온 굽힘강도에 미치는 Y₂O₃의 영향
김해숙(H.S. Kim),안석환(S.H Ahn),손창석(C.S. Son),김종순(J.S. Kim),남기우(K.W Nam) 한국동력기계공학회 2007 한국동력기계공학회 학술대회 논문집 Vol.- No.-
The four kinds of Al₂O₃ composite ceramics were prepared using a mixture of 85 wt.% Al₂O₃ (mean size 0,5 ㎛), 15 wt.% SiC powder with Y₂O₃ as an additive powder (0, 1, 3 and 5 wt.%), The crack-healing strengths were studied as functions of crack-healing temperature and amount of Y₂O₃. The in-situ crack-healing behavior was observed at 1,573 K for 1 h in the air. The heat treated specimen with 3 wt.% of Y₂O₃ showed better crack-healing ability than specimen with 1 or 5 wt.% of Y₂O₃. In case of specimen with 3 wt.% of Y₂O₃, the bending strength of the crack-healed specimen at 1,473 K was recovered to the bending strength of smooth specimen treated at 1573 K. The heat-resistance limit temperature of Al₂O₃ composite ceramics was 1,073 K, 1,373 K, 873 K for the specimen with 1, 3, 5 wt.% of Y₂O₃.
김현수 (H. S. Kim ),김남석 (N. S. Kim ),성기용 (K. Y. Seong ),안석환 (S. H. AHN ),남기우 (K. W. Nam ) 한국동력기계공학회 2009 한국동력기계공학회 학술대회 논문집 Vol.2009 No.6
Oil hydraulic piston pumps are being extensively used in the world, because of simple design, light weight and effective cost etc. An oil hydraulic pump is likely to have serious problems of high leakage, friction and low energy efficiency according to large time use. In the oil hydraulic piston pumps the clearance between the valve block and piston plays an important role for volumetric and overall efficiency. In this paper, the wear property of the SACM645 material used the hydraulic piston pump has been work out by experimentation with variable heat treatment. To investigate the effect according to the piston surface condition, seven different types specimen were prepared.
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.
소결보조재 Al₂O₃ 및 Y₂O₃ 첨가에 따른 Sialon 특성
남기우(K. W. Nam),문석재(S. J. Moon),박승원(S. W. Park),안석환(S.H. Ahn),김종순(J. S. Kim) 한국동력기계공학회 2007 한국동력기계공학회 학술대회 논문집 Vol.- No.-
Various Sialon ceramics were fabricated by hot-pressing mixtures of Si₃N₄, Y₂O₃ and Al₂O₃ powder. The polished specimen of SiAION Ⅰ~Ⅲ showed increased strength by heat treatment, heat treated non-polished specimen were similar or up in strength to polished specimen. The polished specimen of SiAIONN Ⅳ and Ⅴ showed a very high strength, but couldn't obtain increased strength by heat treatment, all specimens were fractured surfaces and inner flaws. Surfaces fractures were initiated from polished surface flaw and comer flaw. inner fractures were initiated from an internal defect.