15,693 research outputs found
The effect of strain rate on the anomalous peak of yield stress in beta-CuZn alloy
No full textX115sciescopu
Acoustic emission characteristics associated with macrostructures and plate orientations of an Al-Li 8090 alloy
No full textAn investigation was carried out to study the microstructural influence on the acoustic emission (AE) behavior during the tensile and fracture tests of an Al-Li 8090 alloy, and to correlate it with the deformation mechanisms of two different microstructures (the delta' microstructure and the S' + delta' microstructure), and of two different orientations (L and S). For the L-oriented specimens, continuous emissions were mostly produced in the delta' microstructure due to the shearing of coherent delta' precipitates, while in the S'+delta' microstructure the burst type emissions were dominant mainly due to the shearing or microcracking of large incoherent S' precipitates as well as the intergranular failure. The S-oriented specimens of both microstructures showed more burst emissions than the L-oriented ones, which resulted from the frequent occurrence of intergranular delamination in the L-oriented specimens. The K-AE values measured by AE method were well agreed with the K-IC values, implying that the K-AE could be considered as a quantitative and reliable parameter to evaluate the fracture toughness of a material. (C) 1997 Elsevier Science S.A.X113sciescopu
Stress induced crystallization of amorphous materials and mechanical properties of nanocrystalline materials: a molecular dynamics simulation study
No full textThe deformation behavior of amorphous and nanocrystalline pure Ni thin films has been investigated using a molecular dynamics simulation study based on a semi-empirical interatomic potential (MEAM). It was observed that a tensile stress introduced to an amorphous material can enhance crystallization which eventually serves as an important deformation mechanism. After completion of crystallization, grains grow mainly by the rotation and coalescence, and with increasing grain size, the flow stress also increases. It was also found that when the grain size is small (below about 3 nm), the dominant deformation mechanisms are the grain rotation and the grain boundary sliding, the former being more active for smaller grains. The dependence of these observations on the interatomic potential used in the simulation is also discussed. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.11sciescopu
Microstructural influence on sag resistance of Cr containing and Cr free spring steels
No full textThe effects of Cr addition and tempering temperature on mechanical properties, especially sag resistance, with respect to the microstructural evolution during tempering in 1.5%Si spring steels, were investigated by performing hardness tests, tensile tests, torsional Bauschinger tests, and examination by transmission electron microscopy. The results obtained showed that the sag resistance depended on the distribution of tempered carbides. With increasing tempering temperature, sag resistance increased to a maximum value at 350 degrees C and then decreased. The CI addition did not affect the behaviour of tempered carbides at low tempering temperatures, while at high temperatures, above 400 degrees C, the Cr addition reduced the coarsening rate of the cementite, resulting in finer particle distribution of the cementite. The Cr addition improved the sag resistance as well as the hardness at tempering temperatures above 400 degrees C, but it decreased the ratio of loop area in the torsional Bauschinger test (the sag resistance) to hardness, regardless of tempering temperature.X11sciescopu
Multisymbol data compression using a binary arithmetic coder
No full textA multisymbol data compression method using a binary arithmetic coder (BAC) is proposed. After representing symbols into a binary format. each bit is sequentially coded by the BAC using a chain rule. The proposed method provides a slightly better compression ratio and much faster processing time than Witten's multisymbol arithmetic coder
Near-lossless/lossless compression of error-diffused images using a two-pass approach
No full textThe current international standard, the Joint Bilevel Image Experts Group (JBIG), is a representative of a bilevel image compression algorithm. It compresses bilevel images with high performance, but it shows relatively low performance in compressing error-diffused halftone images. This paper proposes a new bilevel image compression for error-diffused images, which is based on Bayes' theorem. The proposed coding procedure consists of two passes. It groups 2 x 2 dots into a cell, where each cell is represented by the number of black dots and the locations of the black dots in the cell. The number of black dots in the cell is encoded in the first pass, and their locations are encoded in the second pass. The first pass performs a near-lossless compression, which can be refined to be lossless by the second pass. Experimental results show a high compression performance for the proposed method when it is applied to error-diffused images
Fatigue crack propagation in Al-Li 8090 alloy at room (300K) and cryogenic (77K) temperatures
No full textX1111sciescopu
Quasi-static and dynamic deformation behavior of Ti-6A1-4V alloy containing fine alpha(2)-Ti3Al precipitates
No full textWidmanstatten and equiaxed microstructures containing very fine alpha(2) particles were obtained by aging a Ti-6Al-4V alloy, and their quasi-static and dynamic deformation behavior was investigated in comparison to that of unaged microstructures. Quasi-static and dynamic torsional tests were conducted on them using a torsional Kolsky bar, and torsionally deformed areas beneath fracture surfaces were observed to investigate various microstructural factors determining the deformation behavior and effects of alpha(2) precipitation. The dynamic torsional test results indicated that maximum shear stress and fracture shear strain of the aged Widmanstatten and equiaxed microstructures were higher than those of the unaged microstructures. The number of voids initiated in the aged Widmanstatten and equiaxed microstructures was five times greater than those in unaged microstructures because of the alpha(2) precipitation. This indicated that the aging treatment had a homogenizing effect, i.e., less likelihood of developing a region of concentrated strain that preceded the adiabatic shear band formation, thereby reducing the possibility of the adiabatic shear band formation. Fine alpha(2) precipitation by aging was effective in the improvement of quasi-static and dynamic torsional properties and in the reduction of the adiabatic shear banding, which provided a new idea to improve ballistic performance of Ti alloy armor plates. (C) 2003 Elsevier B.V. All rights reserved.X1140sciescopu
- …
