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31.
Suli Chang Dongkai Shangguan Doru M. Stefanescu 《Metallurgical and Materials Transactions A》1992,23(4):1333-1346
A model of phase transformations in spheroidal graphite (SG) cast iron has been developed to quantitatively describe the microstructural
evolution during solidification and the subsequent solid-state phase transformations (eutectoid reaction) during continuous
cooling and to predict some of the microstructural characteristics of final phases formed in SG iron castings. Such characteristics
include phase fractions, phase spacings, and grain dimensions. In the model, the nucleation and growth of primary dendrites
and eutectics were described based on existing theories, whereas the mathematical formulation for the eutectoid reaction,i.e., the formation of pearlite and ferrite from the as-cast austenite, was developed based on theories as well as physical evidence
obtained from the experimental work. The Johnson-Mehl equation and the Avrami equation were used to calculate the fraction
of transformed phases under continuous cooling conditions. The role of the grain impingement factor used in these two equations
and the significance of the additivity principle in treating nonisothermal transformations were briefly discussed. The latent
heat method was used for the numerical treatment of the release of latent heat during phase transformations. A two-dimensional
finite element code which can be used in either Cartesian or cylindrical coordinates (ALCAST-2D) was used to solve the time-dependent
temperature distribution throughout the metal/mold system. Numerical predictions were validated against experimental results,
and good agreement was obtained.
DONGKAI SHANGGUAN, Previously Assistant Research Engineer, The University of Alabama, 相似文献
32.
Effect of Rare Earths on Tribological Properties of Carbon Fibers Reinforced PTFE Composites 总被引:1,自引:0,他引:1
Carbon fibers (CF) were surface treated with air-oxidation and rare earths (RE), respectively. The effect of RE surface treatment on tensile strength and tribological properties of CF reinforced polytetrafluoroethylene (PTFE) composites was invest/gated. Experimental results revealed that RE was superior to air ox/dation in improving the tensile strength, elongation, and the tensile modulus of CF reinforced PTFE (CF/PTFE) composite. Compared to the untreated and air-oxidated CF/PTFE composite, the RE treated composite had the lowest friction coefficient and specific wear rate under a given applied load and reciprocating sliding frequency. The RE treatment effectively improved the interfacial adhesion between CF and PTFE. With strong interfacial coupling, the carbon fibers carried most of the load, and direct contact and adhesion between PTFE and the counterpart were reduced, accordingly the friction and wear properties of the composite were improved. 相似文献
33.
Daniel T. Rooney Louis Gullo Dongji Xie N. Todd Castello Dongkai Shangguan 《Microelectronics Reliability》2007,47(12):2152-2160
This paper presents a study of the optimization of the gold plating thickness for the use of both wire bonding and soldered interconnects on a flexible printed circuit board sample module. Wire bondability is typically better, when the gold plating thickness is greater than 30 μin.; however, the risk of problems with solder joint embrittlement becomes a concern with thick gold plating. In order to better understand the effect of the gold plating thickness on wire bondability and solder joint embrittlement, an evaluation was performed on samples with three ranges of gold plating thicknesses (10–20 μin., 20–30 μin., and 30–45 μin.), on flexible printed circuit board (PCB), substrates. Mechanical shear testing and metallurgical analyses were conducted on chip component solder joints in this three thickness gold study. Thermal shock and drop testing were conducted to evaluate the reliability of the sample modules. Drop testing is especially critical for determining the reliability of the sample modules, which are used in portable consumer electronics products. Reliability testing and metallurgical analyses have been performed to characterize the effect of gold embrittlement on the mechanical integrity of the solder joints with a gold content ranging from 1 to 4 wt.%. 相似文献
34.
35.
Caolong Li Jian YuanBingyan Han Wenfeng Shangguan 《International Journal of Hydrogen Energy》2011,36(7):4271-4279
Novel CdS nanomaterials were synthesized by a simple “one-pot” hydrothermal biomolecule-assisted method using glutathione (GSH) as the sulfur source and structure-directing reagent. Various morphologies of CdS photocatalysts, such as solid nanospheres (s-CdS), hollow nanospheres (h-CdS) and nanorods (r-CdS), were obtained by controlling only the hydrothermal temperatures. The X-ray diffraction patterns confirmed that all of the samples were typical hexagonal wurtzite CdS. It was found that the absorption edge of s-CdS was at 465 nm with a greater blue shift compared to that of h-CdS and r-CdS. The photocatalytic activity of s-CdS was superior to that of h-CdS and r-CdS under visible light. Photoluminescence measurements revealed their different photogenerated electron/hole recombination ability, which was in accordance with the order of s-CdS < h-CdS < r-CdS. The excellent photocatalytic activity of s-CdS was ascribed to the small sizes of sub-nanocrystallites, which make it easy for photoinduced electrons and holes on the solid sphere to migrate to the surface and react with water and the sacrificial agent quickly. It was crucial to control the temperature for preparing CdS photocatalysts via hydrothermal methods. The formation mechanism of different morphology might be due to complexation, S-C bond rupture, spherical aggregation and Ostwald ripening processes. 相似文献
36.
考虑到巨型箱型柱截面净尺寸大、壁厚、组装隔板多等特点,施工时需控制局部变形及整体变形,以保证构件几何尺寸精度。运用有限元软件,结合117大厦地下室核心巨柱焊接实例,对箱型柱80mm超厚板的焊接温度场及应力场进行动态模拟。计算结果表明:焊接热源的影响区域仅限于焊缝附近区域,而远离焊缝的区域基本维持在室温状态;随着焊接热源的移动,焊缝区域逐步达到屈服状态而发生塑性变形,但钢材仅发生弹性变形;简化模型的周边最大位移在毫米的数量级上,一定程度上可以认为焊接对与模型相连的构件的影响很小。 相似文献
37.
忻州市现有五座中型水库不同程度地存在防洪标准低,坝体填筑质量差,坝基、坝肩渗漏严重,观测、管理配套孕施不健全等问题,结合除险加固工程实践,通过对水库病险成因的分析,阐述了相应的加固措施。 相似文献
38.
The effect of oxygen concentration on the catalytic reaction of NOx with soot over BaAl2O4 has been studied by Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFTS). The introduction of O2 into the NO flow can result in a reactant mixture of NO/NO2/O2. Increasing the O2 concentration from 2 % to 5 % in the NO‐containing flow promotes the formation of NO2 from the gas phase oxidation of NO. The reactant mixture with high O2/NO flow, allows for the formation of greater amounts of nitrate species than that with low O2/NO flow, which further promotes the reaction of soot with NOx and leads to a high conversion efficiency of NOx into N2 and N2O. In the absence of O2, N2O is not observed since the N2O produced at high temperatures has reacted with soot before it can be detected. 相似文献
39.
Shangguan Hao-long Kang Jin-wu Yi Ji-hao Deng Cheng-yang Hu Yong-yi Huang Tao 《中国铸造》2018,15(3):210-215
3D printing technology has been used for sand molding and core printing, but they simply substitute the traditional molding and core making method without changing the shape or size of the sand mold(core) and their dense structure. In this study, a new type of hollow mold based on 3D printing is presented. The new type of mold is a rib reinforced thickness-varying shell mold. This mold design can realize the controlled cooling of castings, i.e., different cooling rates at different areas, and improve the temperature uniformity of a casting after its solidifi cation. Therefore, the performance of castings can be improved and their residual stress and deformation can be reduced. This kind of new mold was applied to a stress frame of A356 aluminum alloy. The 3D printed rib reinforced thickness-varying shell mold was compared with the traditional dense mold, and the castings obtained by these two kinds of molds were also compared. The experimental results showed that the rib reinforced shell mold increased the cooling rate of the casting by 30%, tensile strength by 17%, yield strength by 11%, elongation by 67%, and decreased its deformation by 43%, while sand consumption was greatly reduced by 90%. 相似文献
40.