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31.
Combined with ultrasonic pulse-echo technique, reflection spectrum analysis was introduced to evaluate TiAl and 40Cr diffusion bonding quality. Frequency dependence of reflection coefficient was used to distinguish perfect bonding from imperfect bonding. It is found that the reflection coefficient from perfect bonding interface does not vary with frequency. When the size of imperfections is much smaller than the wavelength of ultrasound, the reflection coeffwient depends on frequency. When the size of imperfections is the same order of or even larger than the wavelength of ultrasound, the reflection coeffwient does not exhibit frequency dependence. However the amplitude of imperfect interface is higher than the amplitude of perfect bonding interface. A combination of reflection spectrum analysis and ultrasonic pulse-echo technique provides more accurate information about the bonding quality of dissimilar materials. 相似文献
32.
J.S.Sun J.Q.Gao Y.Feng Y.W.Luan MOE Key Lab.of Liquid Structure Heredity of Materials Shandong University Ji’nan China Technology Center Ji’nan Iron Steel Group Ji’nan China 《金属学报(英文版)》2004,17(2):189-193
A mathematical model describing the behavior of metal inert gas (MIG) welding isformulated in the paper. By means of numerical simulation, the influence of surface-active elements on fluid flow of MIG weldpool is studied. The calculation resultsshow that by adding surface-active elements, the fluid flow behavior is drasticallychanged and the flow fluid flows from lower to upper in vertical direction at the rearof weldpool (w>0). The physical phenomenon is explained from the viewpoint of fluidflow behavior of weldpool that the properties of weld metal is greatly improved andthe content of diffused hydrogen is reduced, thus providing a basis for developing newwelding materials. 相似文献
33.
34.
研究了采用不同焊接参数时ZL114A铸铝搅拌摩擦焊接头的金相组织、硬度分布及力学性能。结果表明,ZL114A铸铝的搅拌摩擦焊焊接性良好。焊核区的微观组织是无方向性的、细小的等轴晶粒。细化的硅粒子均匀布满整个焊核区。与粗大的树枝状母材相比,焊核晶粒细小、均匀而致密,没有观察到气孔等缺陷。焊缝区硬度分布较母材稳定,变化范围小。随着焊速增加,硅粒子所占体积比逐渐下降。热一机械影响区晶粒被拉长。接头的力学性能与焊接参数的匹配有关系。采用高焊速及转速与焊速比在3左右,获得的接头抗拉强度可达到母材的91%。焊后经T6热处理,可与同炉热处理母材等强。 相似文献
35.
为了探讨GCr15钢的ELID(Electrolytic In-process Dressing)磨削性能,在基于大量实验的基础上,对GCr15钢采用ELID磨削时磨削力的变化规律进行了详细分析,并将磨削力、磨削表面粗糙度与普通磨削进行了比较。结果表明,采用铸铁结合剂CBN砂轮进行ELID磨削时磨削力几乎不随时间的变化而变化,而采用白刚玉砂轮进行磨削时的磨削力随时间的变化不断增大,在线电解修整使CBN砂轮在磨削过程中始终保持良好的磨削性能,有利于节省砂轮修整时间,提高加工效率。在ELID磨削中,采用微细砂轮进行磨削可以获得很低的表面粗糙度,实现对GCr15钢的超精密镜面磨削。 相似文献
36.
The process of friction-stir welding 2A12CZ alloy has been studied. And strength and elongation tests have been performed, which demonstrated that the opportunity existed to manipulate friction-stir welding parameters in order to improve a range of material properties. The results showed that the joint strength and elongation arrived at their maximums ( 331 MPa and 4% ) at 37. 5 mm/min and 300 rpm. As welding parameters changing, joint tensile strength and elongation had similar development. Hardness measurement indicated that the weld was softened. However, there was considerable difference in softening degree for different joint zone. The weld top had lower hardness and wider softening zone than other zone of the weld. And softening zone at advancing side was wider than that at retreating side. 相似文献
37.
A stochastic finite frequency consensus protocol for directed networks with Markov jump topologies and external disturbances is proposed in this paper. By introducing the frequency band information into consensus control design, the disagreement dynamics of interconnected networks asymptotically converge to zero with an improved level of disturbance attenuation in the specific frequency band. In addition, the new model transformation approach is presented by exploring certain features of Laplacian matrix in real Jordan form, which leads to more generality of the designed protocol. A numerical example validates the potential of the developed results. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
38.
After major capacity breakdown(s) on a railway network, train dispatchers need to generate appropriate dispatching plans to recover the impacted train schedule from perturbations and minimize the expected total train delay time under stochastic scenarios. In this paper, we propose a cumulative flow variables-based integer programming model for dispatching trains under a stochastic environment on a general railway network. Stable Train Routing (STR) constraints are introduced to ensure that trains traverse on the same route across different capacity breakdown scenarios, which are further reformulated to equivalent linear inequality constraints. Track occupancy and safety headways are modelled as side constraints which are dualized through a proposed Lagrangian relaxation solution framework. The original complex train dispatching problem is then decomposed to a set of single-train and single-scenario optimization subproblems. For each subproblem, a standard label correcting algorithm is embedded for finding the time dependent least cost path on a space-time network. The resulting dual solutions can be transformed to feasible solutions through priority rules. Numerical experiments are conducted to demonstrate the efficiency and effectiveness of the proposed solution approach. 相似文献
39.
在现有身份认证技术的基础上,研究了一种利用智能手机作为身份认证载体、结合了二维条码和蓝牙技术、具有较高安全性和易用性的身份认证系统,并对系统实现的关键技术进行了研究。 相似文献
40.
栾茜茜 《网络安全技术与应用》2013,(9):110-110,114
随着信息时代的到来,网络信息技术的应用范围越来越广,在学校教学不断改革的过程中,教学中对信息技术的使用越来越普遍。本文主要对网络信息技术在高中体育教学中的应用进行了讨论,首先分析了在高中体育教学中运用网络信息技术的作用,然后介绍了网络信息技术在高中体育教学中具体的应用方式。 相似文献