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RISS 인기검색어
- 검색키워드
- 저자 : Takayuki Hama (검색결과 4 건)
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Crystal Plasticity Finite Element Analysis of Loading-Unloading Behaviour in Magnesium Alloy Sheet
Takayuki Hama,Hitoshi Fujimoto,Hirohiko Takuda 한국소성가공학회 2010 기타자료 Vol.2010 No.6
Magnesium alloy sheets exhibit strong inelastic response during unloading. In this study crystal plasticity finite element analysis of loading-unloading behaviour during uniaxial tension in a rolled magnesium alloy sheet was carried out, and the mechanism of this inelastic response was examined in detail in terms of macroscopic and mesoscopic deformations. The unloading behaviour obtained by the simulation was in good agreement with the experiment in terms of variation with stress of instantaneous tangent modulus during unloading. Variations of activities of each family of slip systems during the deformation showed that the activation of basal slip systems is the largest during unloading, and the slip direction during unloading is opposite from during loading. These results indicated that one of the factors of the inelastic behaviour during unloading is the fact that the basal slip systems are easily activated during unloading because of their low strengths.
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Prediction of Yield Loci for a Magnesium Alloy Sheet using Crystal-Plasticity Finite-Element Method
Takayuki HAMA,Hitoshi FUJIMOTO,Hirohiko TAKUDA 한국소성가공학회 2011 기타자료 Vol.2011 No.8
This paper presents the prediction of yield loci for an AZ31 magnesium alloy sheet using a rate-dependent crystal-plasticity finite-element method. A differential work-hardening behavior was clearly observed; the contour of plastic work was initially rather flattened in the vicinity of equi-biaxial tension, but thereafter severely bulged. The variation of the relative activity of each family of slip systems was examined to investigate the mechanism of the differential work-hardening behavior. During uniaxial tension, the work hardening was determined mainly by the basal slip in the very beginning, while by both the prismatic slip and the basal slip in the subsequent deformation. On the other hand, during equi-biaxial tension, the activity of the basal slip systems was predominant throughout the deformation, while the relative activity of the prismatic slip systems was smaller than that in the uniaxial tension. We concluded that this difference in the relative activities of the slip systems depending on the biaxial-stress ratio eventually resulted in the differential work-hardening behavior of the contour of plastic work. The mechanism that the activity of the prismatic slip systems decreased as the biaxial-stress ratio approached to one was also discussed using a simple analytical model.
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Hayakawa, Kazuichi,Tang, Ning,Sato, Kosuke,Izaki, Akihiko,Tatematsu, Michiya,Hama, Hirotaka,Li, Ying,Kameda, Takayuki,Toriba, Akira Korean Society for Atmospheric Environment 2011 Asian Journal of Atmospheric Environment (AJAE) Vol.5 No.3
1-Nitropyrene (1-NP), 2-NP and 2-nitrofluoranthene (2-NFR) are useful markers for studying the atmospheric behaviors of polycyclic aromatic hydrocarbons (PAHs) and nitropolycyclic aromatic hydrocarbons (NPAHs). However, present methods for measuring trace levels of these compounds are lesssensitive and laborious. Here we describe several improvements to a previously reported high-performance liquid chromatography-chemiluminescence detection system that allows it to determine trace levels of 1-, 2-NPs and 2-NFR. The proposed system was equipped with a reducer column packed with Pt/Rh instead of zinc whose life-time was limited. The combination of Cosmosil MS-II (monomeric ODS) and AR-II (polymeric ODS) columns was used instead of polymeric ODS columns as the separator column to improve the separation. An ethanol mixture with acetate buffer (pH 5.5) was used in place of an acetonitrile mixture with the same buffer to activate the reducer column. The same ethanol mixture was used as the mobile phase for the clean-up column. The switching time of the column switching valve was optimized to concentrate the amino-derivatives of above NPAHs quantitatively on the concentrator column. The concentrations of bis(2,4,6-trichlorophenly) oxalate and hydrogen peroxide in the chemiluminescence reagent solution were optimized to 0.4 mM and 30 mM, respectively, to increase the sensitivity. Under the above conditions, the detection limits (S/N=3) of 1-, 2-NPs and 2-NFR were 1 fmol (0.25 pg), 10 fmol (2.5 pg) and 4 fmol (1 pg), respectively. The proposed system was effectively used to determine trace levels of 1-, 2-NPs and 2-NFR in airborne particulates collected at Noto Peninsula. The atmospheric concentrations of 1-, 2-NPs and 2-NFR were not more than sub pg $m^{-3}$ levels. They were higher in winter (January) than in summer (July). In both seasons, the concentrations were in decreasing order, [2-NFR]>[1-NP]>[2-NP].
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Kazuichi Hayakawa,Ning Tang,Akihiko Izaki,Michiya Tatematsu,Hirotaka Hama,Ying Li,Takayuki Kameda,Akira Toriba 한국대기환경학회 2011 Asian Journal of Atmospheric Environment (AJAE) Vol.5 No.3
1-Nitropyrene (1-NP), 2-NP and 2-nitrofluoranthene (2-NFR) are useful markers for studying the atmospheric behaviors of polycyclic aromatic hydrocarbons (PAHs) and nitropolycyclic aromatic hydrocarbons (NPAHs). However, present methods for measuring trace levels of these compounds are lesssensitive and laborious. Here we describe several improvements to a previously reported high-performance liquid chromatography-chemiluminescence detection system that allows it to determine trace levels of 1-, 2-NPs and 2-NFR. The proposed system was equipped with a reducer column packed with Pt/Rh instead of zinc whose life-time was limited. The combination of Cosmosil MS-II (monomeric ODS)and AR-II (polymeric ODS) columns was used instead of polymeric ODS columns as the separator column to improve the separation. An ethanol mixture with acetate buffer (pH 5.5) was used in place of an acetonitrile mixture with the same buffer to activate the reducer column. The same ethanol mixture was used as the mobile phase for the clean-up column. The switching time of the column switching valve was optimized to concentrate the amino-derivatives of above NPAHs quantitatively on the concentrator column. The concentrations of bis(2,4,6-trichlorophenly)oxalate and hydrogen peroxide in the chemiluminescence reagent solution were optimized to 0.4 mM and 30 mM, respectively, to increase the sensitivity. Under the above conditions, the detection limits (S/N =3) of 1-, 2-NPs and 2-NFR were 1 fmol (0.25 pg),10 fmol (2.5 pg) and 4 fmol (1 pg), respectively. The proposed system was effectively used to determine trace levels of 1-, 2-NPs and 2-NFR in airborne particulates collected at Noto Peninsula. The atmospheric concentrations of 1-, 2-NPs and 2-NFR were not more than sub pg m^-3 levels. They were higher in winter (January) than in summer (July). In both seasons,the concentrations were in decreasing order,[2-NFR]>[1-NP]>[2-NP].
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