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- 저자 : Kawasaki T. (검색결과 12 건)
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Cho, T.S.,Lee, H.J.,Ahn, B.,Kawasaki, M.,Langdon, T.G. Elsevier Science 2014 Acta materialia Vol.72 No.-
Experiments were conducted to examine the evolution of microstructure and mechanical properties in a Zn-22% Al eutectoid alloy processed by high-pressure torsion (HPT). Measurements of the Vickers microhardness revealed significant weakening in the alloy after HPT, and microstructural analysis showed that the initial duplex structure, consisting of equiaxed grains and lamellae, was retained at the disk centers after HPT, whereas equiaxed fine grains were observed at the disk edges. Direct evidence is presented for a transformation of the lamellae into equiaxed very fine grains and subsequent dynamic recrystallization in the early stages of HPT. The reduction of the lamellar structure and the loss of Zn precipitates account for the weakening in the alloy in HPT processing. Excellent high strain rate superplasticity was recorded after HPT, with elongations up to ~1800% at 473K at a strain rate of 10<SUP>-1</SUP>s<SUP>-1</SUP>. The experiments show that the maximum elongations are displaced to faster strain rates with increasing numbers of HPT turns.
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Engineering Carrier Effective Masses in Ultrathin Quantum Wells of IrO2
Kawasaki, Jason K.,Kim, Choong H.,Nelson, Jocienne N.,Crisp, Sophie,Zollner, Christian J.,Biegenwald, Eric,Heron, John T.,Fennie, Craig J.,Schlom, Darrell G.,Shen, Kyle M. American Physical Society 2018 Physical review letters Vol.121 No.17
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유헌일(Heonil Yoo),천기정(T. Kawasaki),택목양삼(Y. Sawaki) 한국자동차공학회 1983 오토저널 Vol.5 No.1
In case of K_lmax < K_lscc, the corrosion fatigue of high strength steel in O.1N H₂SO₄ solution and 3.5% salt water is as follows.<br/> 1. The fatigue life shortens in order of 3.5% salt water and O.1N H₂SO₄ solution.<br/> 2. The fatigue crack growth rate in air is obtained as the following equation.<br/> (dc/dN)_?=7.23×10^-?(△K)^?<br/> 3. The corrosion fatigue crack growth rate in environment is divided into three regions, that is, First Region, Second Region and Third Region from the small cyclic stress intensity.<br/> 4. The formation rate of the active surface on metal is slower than the mechano-chemical reaction rate in First Region. The crack growth rate depends on time and the cyclic stress intensity and is expressed as the following equation.<br/> (dc/dN)=C(△K)^δ<br/> 5. The formation rate of the active surface is faster than the mechano-chemical reaction rate in Second Region and the synergistic effect by stress and corrosion becomes slow. In case the. fatigure load is large, we have the critical crack growth rate which is not<br/> related to the cyclic stress intensity. .<br/> 6. The corrosion crack growth rate by the mechano-chemical reaction is the same in H₂S0₄ solution and salt water, so Hydrogen accelerates the crack growth.<br/> 7. The environment has no effect on the corrosion. fatigue crack growth rate in Third Region.<br/> 8. In First Region and Second Region, dimple is observed on the fatigue fracture surface in O.lN H₂SO₄ solution.<br/> 9. The striation is observed in any environment as in air in Third Region and its interval approximately coincide with the crack growth rate.
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A Diode-Clamped Multilevel Inverter with Voltage Boost Function
Y. Sato,M. Kawasaki,T. Ito 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5
Multilevel inverters are mainly used in high power and medium voltage applications to reduce the required voltage rating of the power semiconductor switching devices. On the other hands, these multilevel inverters are attractive for various applications regardless of the power ratings because they can essentially realize lower harmonics with lower switching frequency and lower electromagnetic interference (EMI). In this context, the multilevel inverters with larger number of levels suitable for circuit integration are actively investigated. Diode-clamped multilevel inverters are regarded as the promising solution. In the diode-clamped multilevel inverters whose number of the levels exceeds three, voltage balancing circuits for the DC capacitors to maintain the proper voltage are indispensable. The authors have been investigated the application of a circuit topology of the voltage balancing circuits so called Resonant Switched Capacitor Converters (RSCC). In the present paper, the utilization of the voltage boost function of RSCC to enhance the allowable range of the input voltage of the inverter is investigated. The voltage boost function is useful in the applications in which the DC source voltage is limited such as batteries and fuel cells. From the computer simulation and the experimental results, the usefulness and the operating characteristics of the voltage boost operation have been demonstrated.
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Shahmir, H.,He, J.,Lu, Z.,Kawasaki, M.,Langdon, T.G. Elsevier Sequoia 2016 Materials science & engineering. properties, micro Vol.676 No.-
<P>A CoCrFeNiMn high-entropy alloy (HEA) was processed by high-pressure torsion (HPT) under 6.0 GPa pressure up to 10 turns at room temperature. It is shown that there is a gradual evolution in hardness with increasing numbers of turns but full homogeneity is not achieved even after 10 turns. Micro hardness measurements reveal that the material reaches a saturation hardness value of similar to 4.41 GPa and in this condition the microstructure shows exceptional grain refinement with a grain size of similar to 10 nm. An ultimate strength value of similar to 1.75 GPa and an elongation to fracture of similar to 4% were obtained in a sample processed for 5 turns. The nanostructured HEA was subjected to post-deformation annealing (PDA) at 473-1173 K and it is shown that the hardness increases slightly to 773 K due to precipitation and then decreases up to 1173 K due to a combination of recrystallization, grain growth and a dissolution of the precipitates. The formation of brittle precipitates, especially sigma-phase, at 873 and 973 K significantly reduces the ductility. Short-term annealing for 10 min at 1073 K prevents grain growth and leads to a combination of high strength and good ductility including an ultimate tensile strength of similar to 830 MPa and an elongation to failure of similar to 65%. (C) 2016 Elsevier B.V. All rights reserved.</P>
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Zhou, W.,Yamamoto, G.,Fan, Y.,Kwon, H.,Hashida, T.,Kawasaki, A. Pergamon Press ; Elsevier Science Ltd 2016 Carbon Vol.106 No.-
<P>Quantitative characterization of interfacial shear strength (IFSS), in multi-walled carbon nanotube (MWCNT)-reinforced Al matrix composites, has been carried out using an in-situ pull-out technique. The end of an MWCNT protruding out of the tensile fracture surface of the composite was bonded to the tip of an atomic force microscopy (AFM) cantilever using an electron-beam-induced deposition method. The MWCNT was pulled out from the Al matrix using a nanomanipulator system installed inside a scanning electron microscope (SEM). The effective embedded length of the MWCNT incorporated in the Al matrix was evaluated by observing the pulled out MWCNT under high-resolution transmission electron microscopy (HRTEM). Valid results were obtained for six MWCNTs with straight, visibly damage-free embedded parts nearly perpendicular to the fracture surface. The IFSS between the MWCNT and the Al matrix was 24.8 +/- 3.2 MPa. The ultimate tensile strength (UTS) of the MWCNT/Al composites is in good agreement with that estimated by the shear lag model using these IFSS values, resulting in the realization of 60% load transfer efficiency at the directly contacted MWCNT-Al interface in the MWCNT/Al composites. No MWCNT failure was observed during the pullout in this study. (C) 2016 Elsevier Ltd. All rights reserved.</P>
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Park, D.Y.,Sakamoto, H.,Kirley, S.D.,Ogino, S.,Kawasaki, T.,Kwon, E.,Mino-Kenudson, M.,Lauwers, G.Y.,Chung, D.C.,Rueda, B.R.,Zukerberg, L.R. American Association of Pathologists and Bacteriol 2007 The American journal of pathology Vol.171 No.5
Cables is a cyclin-dependent kinase-binding nuclear protein that maps to chromosome 18q11-12. Here, we assessed Cables expression in 160 colorectal cancers (CRCs), its role in colon cancer cell growth, and the potential mechanisms of Cables inactivation. Expression levels, promoter methylation, and mutational status of Cables were investigated in colon cancer cell lines and primary colon tumors. Chromosome 18q loss of heterozygosity (LOH) was evaluated with multiple polymorphic markers. Cables inhibited cellular proliferation and colony formation in colon cancer cell lines. Cables expression was reduced in 65% of primary CRCs. No mutations were detected in 10 exons of Cables in 20 primary colon tumors. Cables promoter was methylated in cell lines with decreased Cables expression and vice versa. 5-Aza-2'-deoxycytidine resulted in increased Cables expression in methylated cell lines. There was a significant correlation between promoter methylation and Cables gene expression in primary colon tumors. Sixty-five percent of primary colon tumors demonstrated chromosome 18q LOH. LOH involving the Cables region was observed in 35% of cases, including those in which more distal portions of chromosome 18q were retained, and Cables expression was decreased in all such cases. Loss of Cables expression in 65% of CRCs suggests that it is a common event in colonic carcinogenesis, with promoter methylation and LOH appearing to be important mechanisms of Cables gene inactivation.
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Rapid synthesis of an extra hard metal matrix nanocomposite at ambient temperature
Ahn, B.,Zhilyaev, A.P.,Lee, H.J.,Kawasaki, M.,Langdon, T.G. Elsevier Sequoia 2015 Materials science & engineering. properties, micro Vol.635 No.-
The strengthening of metals is essentially controlled by the microstructures of the metal solids and it is well understood that smaller grain sizes lead to higher hardness and increased strength. Nevertheless, true bulk nanostructured materials are difficult to produce using established engineering techniques, especially when considering the practical and societal needs of materials selection. Lightweight Al and Mg are conventional metals having excellent physico-chemical and mechanical properties and with good strength/weight ratios in the finished products. However, the fabrication of high-strength metals consisting of these elements, using mechanical alloying and milling and cladding-type metal working, generally involves long-term processing conducted under extreme conditions using special facilities. The present study demonstrates the very rapid synthesis of a metal matrix nanocomposite (MMNC) of the Al-Mg system which was achieved by stacking metal disks of the two pure metals and processing by high-pressure torsion at ambient temperature for 10 turns. An exceptionally high hardness was achieved, similar to many steels, through rapid stress-induced diffusion of Mg and the simultaneous formation of intermetallic nano-layers and a nanostructured intermetallic compound with a supersaturated solid solution. This unexpected result suggests a potential for simply and expeditiously fabricating a wide range of MMNCs.
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High-cycle fatigue behavior of Zn-22% Al alloy processed by high-pressure torsion
Choi, I.C.,Yoo, B.G.,Kraft, O.,Schwaiger, R.,Seok, M.Y.,Kawasaki, M.,Langdon, T.G.,Jang, J.i. Elsevier Sequoia 2014 Materials science & engineering. properties, micro Vol.618 No.-
A Zn-22% Al eutectoid alloy was processed by high-pressure torsion (HPT) and its high-cycle fatigue behavior was explored using novel small-scale bending fatigue experiments. Testing of the finest grain region in each HPT disk showed that the fatigue life decreases continuously with increasing numbers of torsional revolutions. The results are discussed in terms of the HPT-induced hardness change and the underlying fatigue failure mechanism.
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