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Thermal Stress Analysis of Welded Joint in 1420 Al-Li Alloy Induced by Thermal cycling

Journal of Materials Science & Technology 2003年第z1期19卷 205-208页

作者： Hongbin GENG Song HE Dezhuang YANG Space Materials and Environment Engineering Lab. Harbin Institute of Technology Harbin 150001 China Space Materials and Environment Engineering Lab. Harbin Institute of Technology Harbin 150001 China Space Materials and Environment Engineering Lab. Harbin Institute of Technology Harbin 150001 China

A model of double grains under plane stress state has been established. According to the double grain model, thermal stress induced by thermal cycling in welding fusion zone is numerically simulated by finite element method, and the microstructures before and after thermal cycling are observed. The effect of thermal stress on weld microstructure is discussed. Experimental and analysis results show that the difference between the coefficients of thermal expansion and elastic modulus for grains along different crystal directio n can produce alternate thermal misfit stress and strain near boundaries under thermal cycling. At the temperature of upper and lower limit, thermal stress nearby grain boundary reaches maxima. Thermal stress induced changes in microstructure, which expressed by the sending dislocations from boundaries to matrix, piling up against the boundaries and the increasing of dislocation density.

关键词： Thermal cycling, Al-Li alloy, Weld, Microstructure, Finite element method

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Carbon cycling of alpine tundra ecosystems on Changbai Mountain and its comparison with arctic tundra

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Science China Earth Sciences 2002年第10期45卷 903-910页

作者：代力民孔红梅邓红兵吴钢邵国凡赵景柱

The alpine tundra on Changbai Mountain was formed as a left-over ‘island' in higher elevations after the glacier retrieved from the mid-latitude of Northern Hemisphere to the Arctic during the fourth ice age. The alpine tundra on Changbai Mountain also represents the best-reserved tundra ecosystems and the highest biodiversity in northeast Eurasia. This paper examines the quantity of carbon assimilation, litters, respiration rate of soil, and storage of organic carbon within the alpine tundra ecosystems on Changbai Mountain. The annual net storage of organic carbon was 2092 t/a, the total storage of organic carbon was 33457 t, the annual net storage of organic carbon in soil was 1054 t/a, the total organic carbon storage was 316203 t, and the annual respiration rate of soil was 92.9% and was 0.52 times more than that of the Arctic. The tundra-soil ecosystems in alpine Changbai Mountain had 456081 t of carbon storage, of which, organic carbon accounted for 76.7% whereas the mineral carbon accounted for 23.3%.

关键词： carbon cycling, alpine tundra, Changbai Mountain.

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Enhancement on Fatigue Property of Aluminum Alloy Welded Joint by Utilizing Trailing Peening

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Journal of Materials Science & Technology 2003年第z1期19卷 198-201页

作者： Changli WANG Zhimin WAN Min ZHAO Jitai NIU Harbin Institute of Technology Harbin 150001 China Harbin Institute of Technology Harbin 150001 China Harbin Institute of Technology Harbin 150001 China Harbin Institute of Technology Harbin 150001 China

The fatigue properties of 2024T3 aluminum alloy welded joint treated by different peening methods were examined. The different effects on fatigue performance of high strength aluminum welded joints were compared with each other by carry out a series tests using two different peening treatment samples. Results show that by applying synchronized hammer peening to the weak part of joint when weld was going on, trailing peening, may refine the grains near weld line, hardening the surface of weld toe and amend the distribution of residual stress. Because of these results the position of fracture of joint was moved from weld toe to weld line. Compared to the joints treated by peening after welding, the fatigue strength of weld joint treated by trailing peening was enhanced by more than 102%.

关键词： Fatigue strength, cycling, Residual stresses, Trailing peening

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Vertical distribution of phosphorus and P-dissolving/ decomposing bacteria in the sediment of Guanting reservoir

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Science China Earth Sciences 2005年第Z2期48卷 285-294页

作者： LI Cui, YUAN Hongli & HUANG Huaizeng College of Biological Sciences, Key Laboratory of Agro-Microbial Resource and Application, Ministry of Agriculture, China Agricultural University, Beijing 100094, China National Research Center of Geoanalysis, Beijing 100037, China College of Biological Sciences Key Laboratory of Agro-Microbial Resource and Application Ministry of Agriculture China Agricultural University Beijing 100094 China National Research Center of Geoanalysis Beijing 100037 China

In this study, we determined pH, phosphorus content and the number of P-dis- solving/decomposing bacteria in relation to the depth in the sediment of Guanting reservoir in Beijing. The pH value was slightly increased from 8.0 in the surface to 8.5 in the bottle (69 cm in depth) of sediment. The highest P content, 1269 mg/kg, was detected in the 35 cm layer, followed by the 5 cm (993 mg/kg) and 69 cm (580 mg/kg) layers. The number of inorganic P-dissolving bacteria varied from 6(102 to 8(104 and the organic P-discomposing bacteria were from 1.9(103 to 6.3(104 per gram sediment in different depths, which were counted under 28℃ and 20℃ ( pH7.5 and 8.5. The number of P-dissolving/discomposing bacteria was directly correlated to the P content in each layer of sediments. The analysis of P-dissolving/decomposing ability of bacteria showed that some of these bacteria were also capable of accumulating P intracellularly. The intracellular P-accumulation was more efficient at lower temperature; in contrast, the activity of P-dissolving/decomposing was stronger at higher temperature. So the content of dissolved P in water body, or quality of water, could be affected by the change of temperature via the regulation of bacterial activity. On the basis of 16S rDNA sequencing, the 13 efficient P-dis- solving/decomposing bacteria were identified as Bacillus spp., Bacterium sp., Microbacterium sp., Paenibacillus sp. and Pseudomonas sp.

关键词： Guanting reservoir, sediment, P-dissolving/decomposing bacteria, phosphorus cycling, eutrophication.

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Exchange flux of total gaseous mercury between air and natural water surfaces in summer season

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Science China Earth Sciences 2002年第3期45卷 211-220页

作者：冯新斌 Jonas Sommar Katarina Grdfeldt OliverLindqvist State Key Laboratory of Environmental Geochemistry Institute of Geochemistry Chinese Academy of Sciences Guiyang 550002 China Department of Inorganic Chemistry Goteborg University S-412 96 Goteborg Sweden

The exchanges of mercury between surface and air are of significance in the biogeochemical cycling of Hg in the environment, but there are still few reliable data on air/surface exchange in aquatic systems. Field measurement campaigns over seawater surface at Kristineberg Marine Research Station (KMRS) and over Hovg?rds?n River surface at Knobesholm in southwestern Sweden were conducted to measure mercury flux using a dynamic flux chamber technique coupled with automatic mercury vapor-phase analyzers. Both sites show net emissions during summer time. Mercury fluxes measured over both river and seawater surfaces exhibit a consistently diurnal pattern with maximum fluxes during the daytime period and minimum fluxes during the nighttime period. At freshwater site, mercury flux is strongly correlated with the intensity of net solar radiation, and negatively correlated with relative humidity. A typical exponential relationship between mercury flux and water temperature was observed at freshwater measurement site. At seawater site, a strong correlation between mercury flux and intensity of solar radiation was obtained. The driving force of mercury emission from water surface to air is the super-saturation of dissolved gaseous mercury in aqueous phase.

关键词： flux chamber, mercury, DGM, biogeochemical cycling, exchange flux.

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