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31.
Fadi K. Abu-Farha Marwan K. Khraisheh 《Journal of Materials Engineering and Performance》2007,16(2):192-199
As the lightest constructional metal on earth, magnesium (and its alloys) offers a great potential for weight reduction in
the transportation industry. Many automotive components have been already produced from different magnesium alloys, but they
are mainly cast components. Production of magnesium outer body components is still hindered by the material’s inferior ductility
at room temperature. Magnesium alloys are usually warm-formed to overcome this problem; however, it was observed that some
magnesium alloys exhibits superior ductility and superplastic behavior at higher temperatures. More comprehensive investigation
of magnesium’s high temperature behavior is needed for broader utilization of the metal and its alloys. In this work, the
high temperature deformation aspects of the AZ31B-H24 commercial magnesium alloy are investigated through a set of uniaxial
tensile tests that cover forming temperatures ranging between 23 and 500 °C, and constant true strain rates between 2 × 10−5 and 2.5 × 10−2 s−1. The study targets mainly the superplastic behavior of the alloy, by characterizing flow stress, elongation-to-fracture,
and strain rate sensitivity under various conditions. In addition, the initial anisotropy is also investigated at different
forming temperatures. The results of these and other mechanical and microstructural tests will be used to develop a microstructure-based
constitutive model that can capture the superplastic behavior of the material.
This article was presented at the AeroMat Conference, International Symposium on Superplasticity and Superplastic Forming
(SPF) held in Seattle, WA, June 6–9, 2005. 相似文献
32.
Simaan M. Abou Rizk 《Computer-Aided Civil and Infrastructure Engineering》1993,8(5):343-353
Abstract: A stochastic simulation model of a project management game was developed to assist in training estimators in developing bidding strategies in construction. This paper discusses the development of the conceptual gaming model for bidding on construction projects and the implementation of the model on portable software. The model simulates the actual bidding in construction by creating projects, initiating random phenomena, and keeping track of the performance of the individual players of the game. Upon conclusion of the game the winner is selected as the player that maximizes his relative return on the original investment assigned to him by the game. The paper describes the underlying construction management concepts and the bidding process in general. The database management model is then detailed focusing on the requirements and strategy behind the development of the various databases. The paper also describes the various models utilized in simulating the involved random processes. Finally the operation of the program is introduced and its use in educating construction engineers and managers is highlighted. 相似文献
33.
Zhen Zhang Randall E. Scarberry Marwan A. Simaan 《International journal of imaging systems and technology》1998,9(5):351-355
Texture orientation is one of the most important attributes used in biomedical and clinical image interpretation. It provides critical clues of continuity and connectivity useful in relating adjacent image areas. We report a novel approach in which image data are convolved with directional convolution masks and the results are used as input to an artificial neural network for classification of image areas into a number of discrete texture orientation classes. © 1998 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 9, 351–355, 1998 相似文献
34.
Fadi K. Abu-Farha Marwan K. Khraisheh 《Journal of Materials Engineering and Performance》2007,16(2):142-149
The simplest test in characterizing the behavior of superplastic materials is the uniaxial tensile test. Since superplasticity
is achieved at relatively high temperatures, heat involvement adds so many unpredictable problems to the simplest testing
technique. In spite of the vast number of research activities directed towards studying the various aspects of superplastic
deformation, there is a lack of a standardized testing procedure that can tackle the various issues associated with high temperature
testing. In this work, we attempt to shed some light on the controversial issues associated with high temperature superplastic
testing. The effects of various testing procedures and parameters on the accuracy of the results are investigated. We address
the issues related to gripping and test sample geometry, heat and temperature effects, and comment on the available testing
and analysis procedures. We hope that this study highlights the urgent need to develop a standardized testing approach that
takes into account all the important issues affecting high temperature testing.
This article was presented at the AeroMat Conference, International Symposium on Superplasticity and Superplastic Forming
(SPF) held in Seattle, WA, June 6–9, 2005. 相似文献
35.
Karl Stoppek-Langner José Goldwasser Marwan Houalla David M. Hercules 《Catalysis Letters》1995,32(3-4):263-271
The interaction of Mo with zirconia has been investigated by infrared spectroscopy (IR) and carbon dioxide chemisorption. Quantitative analysis of the IR results indicated that Mo interacts preferentially with the most basic hydroxyl group (high frequency band at 3775 cm–1). An approximately 79% decrease in the 3775 cm–1 band is observed vs. 21% for the low frequency band at 3673 cm–1, with increasing the Mo loading up to 1 wt%. The relative decrease of the IR band at 3775 cm–1 was identical to that measured for the CO2 uptake. The Mo cross-sections estimated from CO2 chemisorption results were much higher than those typically reported for the Mo system. It was concluded that, as previously reported for the Mo/Al2o3 system, CO2 chemisorption overestimates the surface coverage of Mo/ZrO2 catalysts. 相似文献
36.
This paper reports on the effect of buoyancy ratio due to both heat and mass transfer on natural convection in a porous enclosure between two isothermal concentric cylinders of rhombic cross sections. For negative values of the buoyancy ratio, buoyancy forces due to heat and mass transfer are in opposite directions (opposing mode), while for positive values they are in the same direction (aiding mode). Numerical results demonstrate that the flow strength increases as the absolute value of the buoyancy ratio increases. In the opposing mode, the eye of the vortex flow is located in the lower half of the enclosure, while in the aiding mode it is positioned in the upper part of the annulus. The average Nusselt and Sherwood number values increase as the absolute value of the buoyancy ratio moves away from 1, with values obtained in the aiding mode being higher than corresponding values achieved in the opposing mode. A comparison is also made between the computed average Nusselt and Sherwood number values and similar ones obtained in a circular annulus having the same inner and outer perimeters as the rhombic enclosure. Predictions indicate large percent difference in values, demonstrating that circular geometries cannot be exploited to accurately predict heat and mass transfer in complex geometries. 相似文献
37.
Sayed S. Abd El Rehim Saad M. Abd El Wahaab Magdy A. M. Ibrahim Marwan M. Dankeria 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1998,73(4):369-376
Electroplating of cobalt onto steel substrates from citrate baths has been investigated under different conditions of bath composition, current density, pH and temperature. A detailed study has been made of the influence of these variables on the potentiodynamic cathodic polarization curves, cathodic current efficiency and the throwing power as well as the throwing index of these baths. The optimum bath composition has been established and it contains: CoSO4.7H2O (0·36 mol dm−3) trisodium citrate (0·19 mol dm−3) and citric acid (0·1 mol dm−3) at pH 5·0. The microhardness of cobalt electrodeposited from citrate baths is high and it may be, under certain conditions, two or three times higher than that reported for cobalt electrodeposited from other different baths. The surface morphology of the as-plated cobalt was investigated by using scanning electron microscopy (SEM) while the structure was studied by using X-ray diffraction analysis and anodic stripping voltammetry (ASV) techniques. © 1998 Society of Chemical Industry 相似文献
38.
39.
Research efforts have reported on the ability of carbon nanotubes (CNTs) to enhance the stiffness and strength of carbon fiber composites. Systematic design of blast-resistant composites requires considering CNTs–carbon composites characteristics and the uncertainty of blast events. This article suggests a systematic reliability-based design approach where system reliability is used to compute the probability of failure of a composite laminate. A case study for the design of a five-layer composite laminate incorporating CNTs and subjected to uncertain blast event is demonstrated. 0.5–1% CNTs contents by weight seem capable of significantly reducing the composite probability of failure during blast. 相似文献
40.
Gautam Gupta Ali Zbib Ahmed El-Ghannam Marwan Khraisheh Hussein Zbib 《Composite Structures》2005,71(3-4):423-428
A novel bioactive, porous silica–calcium phosphate nanocomposite (SCPC) that can be used to treat large bone defects in load-bearing positions has been tested and has shown great potential for applications in tissue engineering. Porosity is essential to the performance of the composite material as a tissue engineering scaffold, as porous scaffolds provide a physical, 3-D template to support new tissue formation. However, porosity characterization using conventional techniques such as porosimetry or scanning electron microscopy requires extensive preparation of samples and may destroy important features during preparation and analysis stage. In this work, the new composite is characterized using an advanced high resolution X-ray computed tomography, which is a non-destructive testing technique that allows construction of the 3-D topology of the microstructure. The results clearly show the effectiveness and versatility of this technique in characterizing the porous architecture of the novel composite biomaterial. The pore distribution, morphology and interconnectivity in the composite scaffolds were found to be ideal for use in tissue engineering applications. 相似文献