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Itakura, Mitsuhiro; Kadoyoshi, Tomoko*; Kaburaki, Hideo; Jitsukawa, Shiro
no journal, ,
Molecular dynamics and quasi-two dimensional dislocation dynamics simulations have been performed to find the hardening mechanism of FCC metals due to irradiation. The focus of this simulation has been placed on the effects of the dissociation of a dislocation in FCC metals and of density, distribution, and strength of pinning centers on the stress-strain relation. Molecular dynamics method is applied to find the behavior of the interaction of an edge or a screw dislocation with a pinning center, such as a rigid sphere or irradiation-induced hexagonal interstitial cluster, and to measure its pinning strength by deriving the stress-strain relation.
Yamaguchi, Masatake; Nishiyama, Yutaka; Shiga, Motoyuki; Kaburaki, Hideo
no journal, ,
First principles method is applied to assess the embrittlement mechanism of bcc iron Fe grain boundaries due to the segregation of sulfur S and phosphorus P mpurities. A simulation method based on the first principles calculations has been proposed and applied to clarify this mechanism. This method is applied to the bcc Fe ymmetrical tilt grain boundary to evaluate the effects of S and P segregation on the embrittlement. For the case of S segregation, we have found that the presence of a small amount of S atoms, nearly 20 to 30 ppm in the bulk, causes a strong embrittlement of a grain boundary, that is, the tensile strength reduces to one tenth of that of a clean grain boundary due to the strong repulsion between sulfur atoms. For the P segregation, depending on the condition of segregation, the reduction of the grain boundary strength is within 10 to 20 percent of the clean grain boundary.
Shimizu, Futoshi; Ogata, Shigenobu*; Kaburaki, Hideo; Li, J.*
no journal, ,
Most bulk metallic glasses (BMG) yield at about 2% strain in uniaxialtension/compression test. A careful analysis of the elementary shearbehavior in contrast to crystalline concepts such the generalized stacking fault (GSF) energy reveal a particularly simple and direct explanation. We perform molecular dynamics (MD) simulations on 2-component model systems and a 5-component BMG system, observing and characterizing the nucleation and evolution of shear bands. Despite gross uncertainties in the interatomic interactions and the pre-deformation glass structure, our MD results give a reasonable account of the 2% universal yield point. The general concepts of glass rejuvenation and aging, which we call alienation and recovery process in the context of intense localized shear, and occurring mainly within a timescale of 1-100 atomic vibration periods, is postulated to play acritical role. This theory (various points has also been proposed byothers) can explain why the yield point is relatively insensitive to the interatomic potential and the structure of the pre-deformed glass.