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排序方式: 共有118条查询结果,搜索用时 11 毫秒
1.
C.T. Chang Y.C. Du R.K. Shiue C.S. Chang 《Materials Science and Engineering: A》2006,420(1-2):155-164
Microstructures and fracture behaviors of infrared heated, vacuum brazed Ti–6Al–4V and Ti-15-3 alloys using two Ti–Cu–Ni braze fillers have been characterized to establish the effects of brazing process parameter and chemical composition on the strength of brazed joints. The brazed joint initially contains two prominent phases; a Ti alloy matrix alloyed with V, Cr, Ni, Cu and Al and a Cu–Ni-rich Ti phase. Brazing temperature and soak time control the amount of Cu–Ni-rich Ti phase in the brazed joints. The fracture mode changes from brittle cleavage to quasi-cleavage to ductile dimple as the amount of Cu–Ni-rich Ti phase is reduced in the brazed joint. Both brazing temperature and soak time are critical to eliminate the Cu–Ni-rich Ti phase for optimal shear strength and ductile fracture of brazed joints. A post-brazing annealing at lower temperature is also shown to be an effective way to homogenize the microstructure of brazed joint for improved joint strength. 相似文献
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Infrared dissimilar brazing of α2-Ti3Al and Ti–6Al–4V using Ti–15Cu–25Ni and Ti–15Cu–15Ni filler metals has been performed in this study. The brazed joint consists primarily of Ti-rich and Ti2Ni phases, and there is no interfacial phase among the braze alloy, α2-Ti3Al and Ti–6Al–4V substrates. The existence of the Ti2Ni intermetallic compound is detrimental to the bonding strength of the joint. The amount of Ti2Ni decreases with increasing brazing temperature and/or time due to the depletion of Ni content from the braze alloy into the Ti–6Al–4V substrate during brazing. The shear strength of the brazed joint free of the blocky Ti2Ni phase is comparable with that of the α2-Ti3Al substrate, and strong bonding can thus be obtained. 相似文献
4.
Abstract For focusing the elliptical Gaussian beam directly, the effects of a non-circular aperture on the focusing properties are studied. The focusing properties for different shapes of apertures, which include a circle, an ellipse and a rectangle, are calculated and compared. Moreover, for different elliptical Gaussian beams, an empirical aperture selection rule that can be used to circularize the focusing spot is proposed. The energy transmission ratios are also considered in this paper. 相似文献
5.
A number of defensive technologies have been proposed for the prevention of security threats. However, these defensive technologies are implemented independently without cooperation among various network domains. In this paper, different administrative networks are leagued to form a federative network environment called a trusted domain. From the perspective of a network manager, there is a need to integrate diverse technologies into an effective defensive system among mutually trusted domains. An imperative task for security management is to put in place a shared defensive mechanism, or protective shield, for multiple domains. A cooperative approach to provide such a shared defensive system is presented with integration of both intra‐domain and inter‐domain defensive mechanisms. The simulation results show that, through sharing the defensive information, the firewall system can successfully detect and filter the repeated intrusions. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
6.
Infrared brazing Ti-6Al-4V and SP-700 alloys using the Ti-20Zr-20Cu-20Ni braze alloy 总被引:1,自引:0,他引:1
Great efforts have been made in brazing high-strength α-β titanium alloys below their beta-phase transformation temperature in order to obtain optimized mechanical properties. The brazing temperature of the cold roll-bonded Ti-20Zr-20Cu-20Ni foil is roughly 70 °C lower than that of Ti-15Cu-15Ni filler metal. Moreover, the detrimental Cu-Ni and Cu-Ni-Zr rich Ti phases can be greatly reduced or eliminated by properly choosing the brazing thermal cycle. This research demonstrates the potential application of Ti-20Zr-20Cu-20Ni foil in brazing titanium alloys. 相似文献
7.
Wang J.R. Engmen E.T. Shiue J.C. Rusek M. Steinmeier C. 《Geoscience and Remote Sensing, IEEE Transactions on》1986,(4):510-516
An experiment was conducted from an L-band syntheticaperture perture radar aboard space shuttle Challenger in October 1984 to study the microwave backscatter dependence on soil moisture, surface roughness, and vegetation cover. The results based on the anlyses of an image obtained at 21° incidence angle show a positive correlation between scattering coefficient and soil moisture content, with a sensitivity comparable to that derived from the ground radar measurements [1]. The surface roughness strongly affects the microwave backscatter. A factor of 2 change in the standard deviation of surface roughness height gives a corresponding change of about 8 dB in the scattering coefficient. The microwave backscatter also depends on the vegetation types. Under the dry soil conditions, the scattering coefficient is observed to change from about -24 dB for an alfalfa or lettuce field to about -17 dB for a mature corn field. These results suggest that observations with a synthetic-aperture radar system of multiple frequencies ies and polarizations are required to unravel the effects of soil ture,oisre, surface roughness, and vegetation cover. 相似文献
8.
A coconut shell activated carbon precursor was modified by impregnation with phosphoric acid. The effects of the particle diameter of the impregnated activated carbons (IACs) on the thickness, pressure resistance, and face velocity of a chemical filter were investigated. Furthermore, volatile organic compounds (VOCs) adsorption experiments were carried out to determine the relationship between the removal efficiency and the chemical properties of the adsorbents. The effects of various parameters such as challenge gas concentration, saturated adsorption ratio, impregnation method and impregnant contents were investigated. The results showed that the effect of face velocity on pressure resistance is larger than that of the thickness, that 0.25 M phosphoric acid impregnation of activated carbon can raise VOC removal efficiency by 2–3% (toluene: from 95.8% to 98.1%, isopropanol: from 95.2 to 97.2%), and that the optimal impregnation time is around 1.5 h. A simple shaking impregnation method exhibited better performance than the ultrasonic method. 相似文献
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The optimization of attribute selection in decision tree-based production control systems 总被引:2,自引:1,他引:1
Yeou-Ren Shiue Ruey-Shiang Guh 《The International Journal of Advanced Manufacturing Technology》2006,28(7-8):737-746
This study develops a learning-based production control system (PCS) to support a manufacturing system to make on-line decisions
that are robust in the face of various production requirements. Selecting essential system attributes (or features) based
on various production requirements to construct PCS knowledge bases is a critical issue because of the existence of a large
amount of shop floor information in a manufacturing system. However, a classical decision tree (DT) learning approach to construct
dynamic dispatching knowledge bases does not consider the optimal subset of system attributes in the problem domain. To resolve
this problem, this study develops a hybrid genetic algorithm/decision tree (GA/DT) approach for DT-based PCS. The hybrid GA/DT
approach is used to simultaneously evolve an optimal subset of system attributes and determine learning parameters of the
DT from a large set of candidate manufacturing system attributes according to various performance measures. For a given feature
subset and learning parameters of a DT decoded by a GA, a DT was applied to evaluate the fitness in the GA process and to
generate the PCS knowledge base. The results demonstrate that the proposed GA/DT-based PCS has, according to various performance
criteria, a better long term system performance than those obtained with classical DT-based PCS and the heuristic individual
dispatching rules, according to various performance criteria. 相似文献