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Incremental Damage Theory of Particle or Short-Fiber Reinforced Composites
Tohgo, Keiichiro,Cho, Young Tae,Ishii, Hitoshi 대한금속재료학회(대한금속학회) 1998 METALS AND MATERIALS International Vol.4 No.3
In particle or short-fiber reinforced ductile-matrix composites, cracking of reinforcements is a significant damage mode because cracked reinforcements lose load carrying capacity. This paper deals with an incremental damage theory of the composites. The composite in damage process contains intact and cracked reinforcements in a matrix. To describe the load carrying capacity of the cracked reinforcement, the average stress of a broken ellipsoidal inhomogeneity in an infinite body is introduced. An incremental constitutive relation of particle or short-fiber reinforced composites including the progressive cracking damage of reinforcements and the plasticity of matrix have been developed based on the Eshelby's equivalent inclusion method and Mori and Tanaka's mean field concept. Influence of the reinforcement damage on the stress-strain response of the composites is demonstrated.
Ito, Atsushi,Kaneko, Tadashi,Miyamoto, Yuka,Ishii, Keiichiro,Fujita, Hitoshi,Hayashi, Tomonori,Sasaki, Masako Korean Society of Photoscience 2002 Journal of Photosciences Vol.9 No.2
A new concept of "photo" -antisense method has been evaluated, where the inhibition of gene expression by the conventional antisense method is enhanced by photochemical binding between antisense oligonucleotides conjugated with photo-reactive compound and target mRNA or DNA. Fluorescein labeled oligodeoxyribonucleotides (F-DNA) was delivered to cell nuclei in the encapsulated form in multilamellar lecithin liposomes with neutral charge. F-DNA was previously shown to photo-bind to the complementary stranded DNA, and the delivery system using neutral liposome to be effective in normal human keratinocytes. In the present study, we used human kidney cancer G401.2/6TG.1 cell line to be advantageous in reproducible experiments. p53 was adopted as a target gene since antisense sequence information has been accumulated. The nuclear localization ofF-DNA was identified by comparing the fluorescence ofF-DNA with that of Hoechst 33258 under fluorescence microscope. After 7hr incubation to accumulate p53 protein induced by UV -B, p53 protein was quantified by Western blot. After 2hrs from F-DNA application, about 30% of cell population incorporated F-DNA in their nuclei with some morphological change possibly due to liposomal toxicity. Irradiation of visible light longer than 400nm from solar simulator at this time enhanced the inhibitory action of antisense F-DNA. The present results suggest that photo-antisense method is promising to control gene expression in time and space dependent manner. Further improvement of F-DNA delivery to cancer cells in the stability and toxicity is in progress. progress.
최성종,권재도,Choe, Seong-Jong,Gwon, Jae-Do,Ishii, Hitoshi 대한기계학회 2001 大韓機械學會論文集A Vol.25 No.7
Atomic Force Microscope (AFM) was used to study cross sectional profiles and dimensions of fatigue striations in 2017-T351 aluminum alloy. Their widths(SW) and heights (SH, SH(sub)h, SH(sub)ι) were measured from the cross sectional profiles of three-dimension AFM images. The following results that will be helpful to understand the fatigue crack growth mechanism were obtained. (1) The relation of SH=$\alpha$(SW)(sup)1.2 was obtained. (2) The ratio of the striation height to its width SH/SW, SH(sub)h/SW and SH(sub)ι/SW did not depend on the stress intensity factor range ΔK and the stress ratio R( =P(sub)min/P(sub)max = K(sub)min/K(sub)max). (3) Effect of precipitate on the morphology of striation was changed by the relative dimensional difference between the striation width SW and the precipitates. From these results, the applicability of the AFM to nano-fractography is discussed.
Evaluation of the Fretting Fatigue Behavior of Ti-6Al-4V Alloy
Kwon, Jae Do,Bae, Yong Tak,Choi, Sung Jong,Chai, Young Suck,Ishii, Hitoshi Trans Tech Publications, Ltd. 2005 Key Engineering Materials Vol.297 No.-
<P>Fretting is a potential degradation mechanism of structural components and equipments exposed to various environments and loading conditions. It is well known that the fatigue life under fretting condition decreases approximately 50-70% compared with that under non-fretting fatigue condition. The specific gravity of titanium alloy is 4.5 which is lighter than steel, however, its specific strength, heat and corrosion resistance are superior to steel. Ti-6Al-4V alloy is a kind of a+b phase titanium alloy, and mechanical properties are changed by alloy elements, shapes and distributions of microstructures. In this study, three different kinds of specimens are prepared under different heat treatments in order to produce different microstructures. Through various kinds of mechanical tests, the following conclusions are observed: 1) The microstructures are observed as equiaxed, bimodal and lamellar microstructures respectively. 2) The elongation percentage is superior for the equiaxed microstructure, and the hardness and tensile strength are superior for the lamellar microstructure. 3) The plain fatigue limit of lamellar structure shows higher value than that of the equiaxed and bimodal structures. 4) The fretting fatigue limit considerably decreases compared with the plain fatigue limit for all materials. 5) The fretting damage of contact surface increases with an increase of cyclic loading amplitude under the constant contact pressure.</P>