Author: Mohamed Osama Abo El-Fotoh
Publisher:
ISBN:
Category :
Languages : en
Pages : 64

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Author:
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ISBN:
Category : Aeronautics
Languages : en
Pages : 992

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Author: Y. V. R. K. Prasad
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ISBN:
Category :
Languages : en
Pages : 7

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Author:
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Category : Nuclear energy
Languages : en
Pages : 992

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NSA is a comprehensive collection of international nuclear science and technology literature for the period 1948 through 1976, pre-dating the prestigious INIS database, which began in 1970. NSA existed as a printed product (Volumes 1-33) initially, created by DOE's predecessor, the U.S. Atomic Energy Commission (AEC). NSA includes citations to scientific and technical reports from the AEC, the U.S. Energy Research and Development Administration and its contractors, plus other agencies and international organizations, universities, and industrial and research organizations. References to books, conference proceedings, papers, patents, dissertations, engineering drawings, and journal articles from worldwide sources are also included. Abstracts and full text are provided if available.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 530

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Author: Richard Morrell Quimby
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ISBN:
Category :
Languages : en
Pages : 1

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An investigation was conducted on the deformation of single crystals of alpha solid solution (12.5 at-% Li in Mg) specially oriented for basal slip. Crystals were tested in tension over the range of temperatures between 77 and 645 K. The alloy has a critical resolved shear-stress at least ten times that of pure Mg. Whereas the critical resolved shear-stress was temperature dependent below 250 K, it was relatively constant over the higher temperature range. Above 400 K all crystals fractured on the prismatic planes following duplex prismatic slip. Twinning, kinking and accommodation bending was observed in areas adjacent to subgrain boundaries and the shear-stress vs shear-strain curves for the crystals were correlated with the various types of deformation markings observed on the surfaces of the strain specimens. The thermally activated deformation mechanism below 250 K probably arises from the dislocation intersection process whereas the higher temperature athermal behavior is thought to be a result of short-range ordering. (Author).

Author: Yuzhi Zhu
Publisher:
ISBN:
Category : Aluminum-magnesium alloys
Languages : en
Pages : 146

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Magnesium, as the lightest structural metal, is attracting researchers' attention in recent years. However, its further application is limited by some shortcomings, like mechanical anisotropy and poor formability, which is ascribed to the low-symmetric HCP structure.The main objective of this dissertation is to unveil the deformation mechanisms of dislocation slip and deformation twinning in rolled AZ31 magnesium alloy during plastic deformation at ambient temperature. Characterization studies by electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM), and theoretical calculations with MATLAB are used to analyze the deformation behaviors.Quasi in-situ EBSD analysis shows that under an unfavorable loading condition for twinning activation, {101Ì52} tensile twins still can be activated but most of them can merely further thicken. While under repeated tensile and compressive strains, the twinning/detwinning process occurs with the sequence of nucleation, propagation, thickening, thinning, shortening, and vanishing. HRTEM analysis shows an intense atomic misalignment near {101Ì52} tensile twin boundaries, especially near the twin tip, ascribed to the mobility of twinning dislocations. TEM analysis also shows that type basal slips are activated at the early deformation stage. type pyramidal dislocations are not observed at low deformation strain but proved to be activated at the late deformation stage. During the whole deformation process, no type prismatic slip is observed by TEM. The Schmid factor analysis explains the phenomena. GND calculation gives us a possibility to evaluate the slip behavior and make it visual in bulk samples. The slip activations depend on both the grain orientations and the strain conditions in the adjunct grains. The increased GND density is accompanied by an increased strain. type basal slips and type pyramidal slips dominate during the deformation process. type prismatic GND density only increases at the late deformation stage. Furthermore, prismatic GNDs prefer to accumulate near grain boundaries and twin boundaries. IGMA analysis explains the slip behaviors in the matrix region and the twinning area. The activation of type prismatic slips inside {101Ì52} tensile twins is easier than that in the matrix region.

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Category :
Languages : en
Pages :

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The effect of strain rate, and particularly of high strain rates, on deformation mechanisms in materials is of fundamental interest to those who model and analyze dynamic loading. In many materials the strain rate sensitivity is known to increase dramatically when the strain rate is raised above approx. 103 s−1. This increase has been interpreted previously as a transmission in deformation mechanism from thermal activation control at low strain rate to dislocation drag control at high strain rate. In copper, copper-aluminum alloys and stainless steel, recent measurements have shown that the increased rate sensitivity found at high strain rates is not due to a transition in deformation mechanism but rather can be explained with standard thermal activation theory. These findings and their implications regarding the formulation of constitutive behavior are presented.

Author: University of California, Berkeley
Publisher:
ISBN:
Category :
Languages : en
Pages : 228

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Author: William Paul Green
Publisher:
ISBN:
Category :
Languages : en
Pages : 168

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Superplastic aluminum alloys have been the subject of recent research in the automotive industry for several reasons. First, the formability of such alloys under superplastic forming (SPF) conditions is quite good; second, the potential weight reduction associated with formed aluminum sheet as compared to traditional steel sheet is particularly important for automotive applications. Unfortunately, SPF-grade aluminum is relatively expensive, and the typical SPF process is expensive and time-consuming because of the high temperatures and slow strain rates involved. The present study investigates the potential for forming AA5083, the most common commercial alloy for SPF operations, at reduced temperatures and increased strain-rates. The deformation and failure mechanisms under these conditions are examined in a modified AA5083 material and are compared with data from unmodified AA5083. A new method of presenting creep transient data is presented and is used to determine deformation mechanisms at elevated temperatures. A modified AA5083 alloy produced by continuous casting (CC), and containing a small addition of Cu, was studied. This small addition of Cu causes the formation of Mg2Cu and MgCu2 intermetallic particles, which produce incipient melting. It is proposed that these low-melting-temperature phases may reside at grain boundaries and enhance grain-boundary sliding at low temperatures, which may explain the improved ductility of the Cu-containing alloy. Ductility variations for the Cu-containing alloy are also explored. The differences in tensile ductility between the Cu-containing AA5083 and unmodified AA5083 materials, produced by both CC and direct-chill (DC) casting, are related to differences in cavitation behavior. The final part of the present work is a study on the effect of various heat treatment schedules on the constituent particle distribution in AA5083. It is shown that a simple one-day aging treatment at a moderate temperature can effectively reduce the interparticle spacing. This may lead to a finer recrystallized grain size [1] and, thus, improve superplastic properties.