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3 tilt grain boundaries under uniaxial compressionShibutani, Yoji*; Hirouchi, Tomoyuki*; Tsuru, Tomohito
Journal of Solid Mechanics and Materials Engineering (Internet), 7(6), p.571 - 584, 2013/06
Microscopic yielding can be realized by the transfer of a dislocation across a grain boundary (GB), or by incorporation between the residual GB dislocation and the dislocations nucleated in the near-field of a GB due to the applied stress. In the present paper, a new boundary interaction criterion of 
- or '-value is proposed, which considers both the contributions of the geometric relationship between two grains and a GB, and the stress state applied to the near-field of a GB. This value and the others so far proposed were calculated for 
110
, 100, and 111 symmetric tilt grain boundaries under uniaxial compression normal to the GB. The dynamic transfer and incorporation of the dislocations nucleated under uniaxial compression normal to the GB plane were then examined using 3-dimensional molecular dynamics simulations.
Suzuki, Hiroshi; Katsuyama, Jinya; Morii, Yukio*
Journal of Solid Mechanics and Materials Engineering (Internet), 6(6), p.574 - 583, 2012/06
Residual stress distributions of 35 mm thick dissimilar butt-weld between A533B ferritic steel and Type 304 austenitic stainless steel (304SS) with Ni alloy welds and similar metal butt-weld of 304SS were measured using neutron diffraction. Effects of differences in thermal expansion coefficients (CTEs) and material strengths on the weld residual stress distributions are discussed by comparison of the residual stress distributions between the similar and dissimilar metal butt-welds. Residual stresses in the similar metal butt-weld exhibited typical distributions found in a thick butt-weld and they were distributed symmetrically on either side of the weld line. Meanwhile, asymmetric residual stress distributions were observed near the root of the dissimilar metal butt-weld, which was caused by differences in CTEs and yield strengths between parent and weld metals. Transverse residual stress distribution of the dissimilar metal butt-weld was similar trend to that of the similar metal butt-weld, since effects of differences in CTEs are negligible, while magnitude of the transverse residual stress near the root depended on the yield strengths of each metal. In contrast, the normal and longitudinal residual stresses in the dissimilar metal butt-weld distributed asymmetrically on either side of weld line due to influence of differences in CTEs.
Nagae, Yuji; Takaya, Shigeru; Asayama, Tai
Journal of Solid Mechanics and Materials Engineering (Internet), 3(3), p.449 - 456, 2009/04
Katsuyama, Jinya; Onizawa, Kunio
Journal of Solid Mechanics and Materials Engineering (Internet), 3(3), p.563 - 571, 2009/00
Welding residual stress, which is one of the most important factors of stress corrosion cracking (SCC) growth in pressure boundary piping, affected by excessive loading such as an earthquake has been evaluated by axisymmetric thermo-elastic-plastic analysis based on finite element method (FEM). Several loading of prescribed displacement for piping butt-welds have been applied in axial direction by varying the loading conditions of maximum value and wave form after welding simulation. Higher excessive loading causes higher relaxation of welding residual stress near piping welds. As the result, SCC growth rate decrease by increasing of prescribed displacement.
Shibata, Taiju; Tada, Tatsuya; Sumita, Junya; Sawa, Kazuhiro
Journal of Solid Mechanics and Materials Engineering (Internet), 2(1), p.166 - 175, 2008/00
To develop non-destructive evaluation methods for oxidation damage on graphite components in High Temperature Gas-cooled Reactors (HTGRs), the applicability of ultrasonic wave and micro-indentation methods were investigated. IG-110 and IG-430 graphites, candidates for Very High Temperature Reactor (VHTR), were uniformly oxidized for experiments. (1) Ultrasonic wave velocities were decreased with increasing the oxidation. It can be expressed empirically by exponential formulas to oxidation weight loss. (2) A wave propagation analysis with a wave-pore interaction model showed slightly less velocity reduction than experimental data of the oxidized IG-110. The possibility of the non-uniform oxidation effect was suggested. (3) Although micro-indentation characteristics were changed to show oxidation-induced degradation, it is necessary to assess the variation of the test data with statistic method to specify the oxidation damage in the next study.
Miwa, Yukio; Kaji, Yoshiyuki; Okubo, Nariaki; Kondo, Keietsu; Tsukada, Takashi
Journal of Solid Mechanics and Materials Engineering (Internet), 2(1), p.145 - 155, 2008/00
In core structural materials of next generation reactors, materials' degradation behavior by neutron irradiation damage and thermal (cyclic) stress should be considered with fair accuracy in design process (including maintenance and repair plans), because the materials are used under higher temperature gradients and higher neutron flux fields than those in the present light water reactors. In the current experiential design rules, service lives of core structural components were determined by the materials degradation such as the increase of ductile-to-brittle transition temperature after post irradiation examination data. However, other materials degradations such as irradiation-assisted stress corrosion cracking (IASCC) should be considered reasonably in the design process of the next generation reactors, because of the anticipation of the beneficial effects by synergistics of these radiation damage such as radiation hardening, local chemical composition change, swelling and radiation creep. To predict material failure by IASCC with reasonable accuracy, in this study, each material degradation phenomenon with different dose dependence was modeled with consideration of radiation induced stress relaxation. The models were integrated to simulate the failure behavior for the reactor operation period. In this paper, the models obtained by ion-irradiation experiments were presented, and the concept of new evaluation method and the programming code for the failure simulation were outlined.
