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991.
Fatigue properties of cast aluminum components are controlled by maximum defect size in the material. The larger the maximum
defect size, the lower the fatigue strength and life. In the presence of casting defects, crack initiation can be ignored
and fatigue life is mainly spent in crack propagation. Therefore, fatigue life of aluminum castings can be predicted by long
or short crack growth models. The main problem is defining a starting defect size from readily available data, such as twodimensional
(2-D) pore size measurements on metallographic sections. In this article, an extremevalue statistics (EVS) method was used
to estimate the maximum defect size in 319 castings from conventional metallographic data. The maximum defect size predicted
by EVS agrees quite well with the initiation defect sizes measured from fracture surfaces, and the predicted fatigue life
is in reasonable agreement with the experimental data. 相似文献
992.
通过对组成打结料成分特性的研究,提出以优质原料生产的MgO-CaO-Fe2O3系合成砂为骨料,用MgO〉97%,粒度〈0.088mm烧结镁砂做细粉,适当添加超微粉等工艺措施,制成适当高碳铬铁电炉炉底用的高基质打结料,通过调控基质成分,实现材料相和固相的复合烧结。 相似文献
993.
Optimal Conditions for Preparing Ultra-Fine CeO2 Powders in A Submerged Circulative Impinging Stream Reactor 总被引:1,自引:0,他引:1
Cerium carbonate powders were produced in a submerged circulation impinging stream reactor (SCISR) from Ce(NO3)3·6H2O. NH4HCO3 was used as a precipitant in the reaction. Cerium carbonate powders were roasted to produce ultra-fine cerium dioxide (CeO2) powders. The optimal conditions of such production process were obtained by orthogonal and one-factor experiments. The results showed that ultra-fine and narrowly distributed cerium carbonate powders were produced under the optimal flowing conditions. The concentrations of Ce(NO3)3 and NH4HCO3 solutions were 0.25 and 0.3 mol·L-1, respectively. The concentration of PEG4000 added in these two solutions was 4 g·L-1. The stirring ratio, reaction temperature, feeding time, solution pH, reaction time and digestion time were 900 r·min-1, 80 ℃, 20 min, 5~6, 5 min and 1 h, respectively. The final product, CeO2 powders, was obtained by roasting the produced cerium carbonate in air for 3 h at 500 ℃. The finally produced CeO2 powders were torispherical particles with a narrow size distribution of 0.8~2.5 μm. The crystal structure of CeO2 powders belonged to cubic crystal system and its space point group was O5H-FM3M. Under optimal conditions, powders produced by SCISR were finer and more narrowly distributed than that by Stirred Tank Reactor (STR). 相似文献
994.
995.
Jinlin Wang 《Components and Packaging Technologies, IEEE Transactions on》2005,28(2):366-370
Flow time is a key material property for underfill materials in flip-chip applications. In this paper, we will discuss how to use flow time testing for underfill flow evaluation and material screening. The flow time of several underfills was measured at elevated temperatures using test pieces made from glass microscope slides. The material properties impacting underfill flow, such as viscosity, contact angle, and surface tension, were also experimentally measured and used to calculate estimated flow times using the Washburn equation. Empirical and calculated flow times were compared. The effects of channel width and flow distance on flow time were also studied. Additionally, the effect of a tilted stage on flow time, epoxy tongue, and void formation was evaluated. 相似文献
996.
InAs channel field-effect transistors of 1-μm gate length were grown by molecular beam epitaxy and observed to operate at channel electric fields (20 kV/cm) higher than previously demonstrated and several times greater than the threshold for impact ionization in bulk InAs. Voltage gains on the order of 10 were observed with transconductances as high as 414 mS/mm and output conductances as low as 33 mS/mm. These voltage gains are comparable to those of GaAs-based devices and are the highest observed for InAs channel devices. The results demonstrate the potential for practical room-temperature operation of InAs FETs 相似文献
997.
998.
Hsueh-Jyh Li Yung-Deh Wang Long-Huai Wang 《Antennas and Propagation, IEEE Transactions on》1996,44(4):444-452
In this paper, how the statistical properties of the matching scores are affected by the carrier frequency, the aspect variation, the range resolution, and the target complexity are studied. The statistical parameters (mean and standard deviation) of the matching scores among range profiles of independent objects are derived, and their values are used as references to determine the threshold values for target identification. It is found that the range profile obtained at a certain carrier frequency can also be used as the feature vector for radars operated at shifted frequencies if the range resolution is fine enough or the target is simple. It is also found that a radar with higher range resolution can tolerate more aspect variation, yielding a significant advantage in saving memory space for establishing the data base. The results obtained can have several applications such as target identification, data association in multiple target tracking, and target direction determination when widely-spaced high-resolution radars are employed 相似文献
999.
1000.