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排序方式: 共有293条查询结果,搜索用时 15 毫秒
51.
52.
Recently, stress corrosion cracking (SCC) has been observed near the welded zone of the primary loop recirculation pipes made of low-carbon austenitic stainless steel type 316L in boiling water reactors. SCC is initiated by superposition effect of three factors. They are material, environmental and mechanical factors. For non-sensitized material such as type 316L, residual stress as a mechanical factor of SCC is comparatively important. In the joining processes of pipes, butt welding is conducted after surface machining. Surface machining is performed in order to match the inside diameter and smooth surface finish of pipes. Residual stress is generated by both processes. Moreover, residual stress distribution generated by surface machining is varied by subsequent welding processes, and it has the maximum residual stress around 900 MPa near the weld metal. The variation of metallographic structure, such as recovery and recrystallization, in the surface machined layer due to the welding thermal cycle is an important factor for this residual stress distribution. In this study, thermal ageing tests were performed in order to evaluate hardness variation due to the thermal cycle in the surface machined layer. Results of thermal ageing tests were applied to the finite-element method as the additivity rule of the hardness variation. Varied hardness was converted into equivalent plastic strain. Then, thermo-elastic-plastic analysis was performed under residual stress fields generated by surface machining. As a result, analytical results of surface residual stress distribution generated by bead-on-plate welding after surface machining show good agreement with measured results by the X-ray diffraction method. The maximum residual stress near the weld metal is generated by the same mechanism as in the both-ends-fixed bar model in the surface machined layer that has high yield stress. 相似文献
53.
Yuji Kosaka Shigeru Kurematsu Takaaki Kitagawa Akihiro Suzuki Takayuki Terai 《Journal of Nuclear Science and Technology》2013,50(10):966-974
The temperature measurements of mixed oxide (MOX) and UO2 fuels during irradiation suggested that the thermal conductivity degradation rate of the MOX fuel with burnup should be slower than that of the UO2 fuel. In order to explain the difference of the degradation rates, the quasi-two phase material model is proposed to assess the thermal conductivity degradation of the MIMAS MOX fuel, which takes into account the Pu agglomerate distributions in the MOX fuel matrix as fabricated. As a result, the quasi-two phase model calculation shows the gradual increase of the difference with burnup and may expect more than 10% higher thermal conductivity values around 75 GWd/t. While these results are not fully suitable for thermal conductivity degradation models implemented by some industrial fuel manufacturers, they are consistent with the results from the irradiation tests and indicate that the inhomogeneity of Pu content in the MOX fuel can be one of the major reasons for the moderation of the thermal conductivity degradation of the MOX fuel. 相似文献
54.
Takumi Chikada Akihiro Suzuki Takayuki Terai Takeo Muroga Freimut Koch 《Fusion Engineering and Design》2013,88(6-8):640-643
Li–Pb compatibility of Er2O3 and Er2O3-Fe two-layer coatings has been explored for an understanding of corrosion behaviors and effects of the protection layer. The coatings were peeled off after static Li–Pb immersion test at 600 °C due to the degradation of adhesion between the coating–substrate interface. A loss of Er and then subsequent corrosion of Er2O3 were shown after immersion at 500 °C for 500 and 1505 h. However, the outer Fe layer played a role to decrease corrosion rate of the coatings by comparing with the results of Er2O3 single layer coatings. Deuterium permeation measurements after corrosion tests at 500 °C showed that the Er2O3 coatings kept permeation reduction factors of 102–103 after 500 h immersion, but seriously degraded after 1505 h immersion. Corrosion mechanisms suggest that corrosion protection properties will be modified by an optimization of the outer Fe layer and a control of oxygen concentration in Li–Pb. 相似文献
55.
A gel‐spinning process was used in an attempt to prepare a gelatin fiber with a high level of drawability. A gel fiber prepared by extrusion of 15 wt % gelatin in dimethyl sulfoxide into methanol at ?20°C was drawn to sixteen times the original length. After extraction of the dispersion medium, the mechanical strength of the fiber increased markedly with the draw ratio, and the fiber exhibited a tensile strength of 146 MPa and a Young's modulus of 2.3 GPa when drawn to the maximum. A gelatin fiber with greater mechanical strength was obtained when ethylene glycol was used as the spinning solvent. The X‐ray diffraction profile indicated the formation of triple‐helical structures and their lateral association, which is responsible for the mechanical strength of the fiber. Heat‐treatment improved the water‐resistance of the prepared fiber. γ‐Irradiation and treatment with glutaraldehyde improved the mechanical strength of the fiber. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
56.
Ryohei Ihara JInya Katsuyama Tadafumi Hashimoto Masahito Mochizuki 《Nuclear Engineering and Design》2011,241(5):1335-1344
In nuclear power plants, stress corrosion cracking (SCC) has been observed near the weld zone of the core shroud and primary loop recirculation (PLR) pipes made of low-carbon austenitic stainless steel Type 316L. The joining process of pipes usually includes surface machining and welding. Both processes induce residual stresses, and residual stresses are thus important factors in the occurrence and propagation of SCC. In this study, the finite element method (FEM) was used to estimate residual stress distributions generated by butt welding and surface machining. The thermoelastic-plastic analysis was performed for the welding simulation, and the thermo-mechanical coupled analysis based on the Johnson-Cook material model was performed for the surface machining simulation. In addition, a crack growth analysis based on the stress intensity factor (SIF) calculation was performed using the calculated residual stress distributions that are generated by welding and surface machining. The surface machining analysis showed that tensile residual stress due to surface machining only exists approximately 0.2 mm from the machined surface, and the surface residual stress increases with cutting speed. The crack growth analysis showed that the crack depth is affected by both surface machining and welding, and the crack length is more affected by surface machining than by welding. 相似文献
57.
Abstract Based on the experimental hydrocracking of vacuum residue, a kinetic study using a lumping model was carried out to gain insight into the characteristics of catalytic reactions. The lumped species were the saturates, aromatics, resins, and asphaltenes (SARA) constituents in the residue (798 K+) fraction and gas, naphtha, kerosene, gas oil, vacuum gas oil, and coke in the products. The pyrite reaction favoring hydrocracking to lighter products was more temperature-dependent than that using a mixture of pyrite and active carbon. The kinetic study showed that the addition of active carbon to pyrite limited the transformation of resins to asphaltenes. 相似文献
58.
Kenji Kanamori Tohru Kineri Ryohei Fukuda Takafumi Kawano Keishi Nishio 《Journal of Materials Science》2009,44(3):855-860
Amorphous ZrW2O8 powder and amorphous SiO2 powder were prepared by a sol–gel process as raw materials, and high-density ZrW2O8–SiO2 were successfully prepared at a much lower temperature of 923 K for a much shorter holding time of 10 min by spark plasma
sintering (SPS) method rather than by conventional melt-quenching method. The relative densities of 0.85ZrW2O8–0.15SiO2 and 0.70ZrW2O8–0.30SiO2 were 99.4% and 96.6%, respectively. The combined technique of a sol–gel process and SPS should enable us to prepare the varied
types of high-density composites of ZrW2O8 without severe thermal cracking caused by melt-quenching. The thermal expansion properties and dielectric properties of ZrW2O8–SiO2 were also investigated. 相似文献
59.
In order to obtain catalyzers to decompose tri-methyl aluminium (TMA) to Al and CH3 at catalyzer temperatures lower than 500 °C, decomposition experiments using Ni-Chrome, Kanthal, Inconel 600, Chromel and SUS-304 catalyzers exhibiting resistance to oxidation have been carried out. The experiments have revealed that TMA can be decomposed to Al and CH3 above 200 °C using Chromel or SUS-304 catalyzer, and that the CH3 does not decompose further below 500 °C. The experiments have also revealed that it requires relatively small activation energy for decomposing TMA to Al and CH3 using Chromel or SUS-304 as the catalyzer. 相似文献
60.
The effect of power interchange operation of multiple household gas engine cogeneration systems (H-GCGS) on the energy-saving is investigated using an optimization approach based on the mixed-integer linear programming. In this power interchange operation, electricity generated by H-GCGS is shared among households in a housing complex without transmitting to a commercial electric power system so that the operating time of these systems may increase. This paper numerically analyzes optimal operational strategies for 20 households and three types of household energy supply configurations: the power interchange operation of the H-GCGSs (IC), stand-alone operation of each H-GCGSs (SA), and conventional energy supply system without the H-GCGSs. A numerical result clarifies the effectiveness of the power interchange operation from the energy-saving viewpoint and a dominant parameter for evaluating the energy-saving effect. 相似文献