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991.
992.
In this study, we perform an experimental result for measurements of the body wave phase and group velocities in transversely isotropic media (TIM) by through-transmission technique. After comparing the experimental and theoretical first arrival times of the waves, a difference between the phase velocity and group velocity is observed. When the ratio between propagation distance (d) of the wave and the diameter (D) of transducer is 2.4 for measuring phase velocity and the point probes configuration for measuring group velocity, the accuracy in velocity estimation can reach the limit of system's resolution. However if d/D is 7.8, the wave will propagate with an intermediate velocity between the phase and group velocities. The rapid change of the wave velocity and waveform for qSV-wave propagation with the group velocity has been observed at the propagation direction near the cusps. Therefore, in order to reduce the error in group velocity estimation of qSV-waves, the optimum directions are suggested at 20 and 60°. 相似文献
993.
介绍了ZG00Cr24Ni20Mo2Cu3超低碳不锈钢锌件的生产过程。根据铸件工艺结构难点和严格的技术条件要求,合理制定了铸造工艺,正确地使用冷铁,成功地生产出合格铸件。 相似文献
994.
Young-Wook Kim Yong-Seong Chun Ji Yeon Park Woo Seog Ryu Dong-Soo Park 《Metals and Materials International》2007,13(3):197-200
A new process using SiC fiber fabrics and SiC tapes to produce dense 2D SiC fiber-SiC (SiC/SiC) composites is demonstrated.
The strategy for fabricating the SiC/SiC composites involves: (i) alternately stacking the SiC fiber fabrics and SiC tapes
at room temperature, (ii) pyrolyzing of the stacked composites, and (iii) hot-pressing the pyrolyzed composites. By controlling
the hot-pressing temperature, it is possible to obtain dense 2D SiC/SiC composites with relative densities of >98%. The 2D
SiC/SiC composites show no degradation of the SiC fibers and a higher mechanical strength. 相似文献
995.
A figure of merit (FOM) has been developed to define the quality of ceramic (e.g., ZrO2) coatings on metal and alloy [Type 304SS and Alloy 600] surfaces. Zirconia (ZrO2) coatings were developed as a means of protecting the metal/alloy surfaces from stress corrosion cracking (SCC) in boiling water reactor (BWR) primary heat transport circuits, by inhibiting the cathodic reaction (reduction of oxygen and hydrogen peroxide) on the surface external to the crack. The distribution of pores in the coating plays an important role in corrosion prevention, such that the lower the porosity of the coating, the better the protection afforded to the system against SCC. Since the reactors operate at high temperature (e.g., at 288 °C under full power conditions), the temperature dependence of the FOM was investigated. The figure of merit (FOM) was developed by measuring impedance data over a wide range of frequency (10 mHz-5 kHz) at temperatures of 25, 100, 200, and 288 °C in hydrogenated, buffered solutions, with the hydrogen electrode reaction (HER) being used as a “fast” redox couple. An “equivalent circuit” analog was first developed from the bare surface impedance data and this analog was then employed in a second step to model the pore bottom in defining the pore distribution on the coated surface. A lognormal distribution (LND) of the pores was assumed and the parameters of the LND were determined using a constrained optimization technique to fit the model to the experimental data for the coated surface at different temperatures. The results suggest that, as temperature increases, the coating becomes more porous, making the substrate more susceptible to corrosion cracking. At 288 °C, 87% of the SS and 85% of the Ni-alloy surfaces become porous with the pore radius varying from 0.0001 cm to 0.01 cm. 相似文献
996.
综述了数控机床热误差模型的研究现状,从热误差模型的类型、优化模型变量建模、综合误差模型、在线热误差模型等方面将已有模型加以分类并进行分析。在此基础上结合我们的工作提出了今后的设想。探讨了数控机床热误差模型研究中尚存在的热误差模型优化问题、模型参数选择问题、边界条件界定问题和在线研究问题以及相关思路。 相似文献
997.
998.
通过对调整螺套模锻成形技术的研究和生产实践,解决了中小型薄壁、深腔、异形大孔的长轴类锻件的模锻成形问题,提高了生产效率和经济效益。 相似文献
999.
1 INTRODUCTION in 1 5 0℃ .Maas[1 0 ] alsomanufacturedtheH2 O2 fuelcellstackswiththeoutputpowerupto 1kW ,andthepropertiesoftheas preparedfuel 相似文献
1000.