The Experts below are selected from a list of 21975 Experts worldwide ranked by ideXlab platform
Xiaoxu Huang - One of the best experts on this subject based on the ideXlab platform.
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dependence of Dislocation Structure on orientation and slip systems in highly oriented nanotwinned cu
Acta Materialia, 2017Co-Authors: Qiuhong Lu, Niels Hansen, Xiaoxu Huang, L LuAbstract:Abstract To explore the correlation between orientation, active slip systems and Dislocation Structure, highly oriented nanotwinned Cu has been deformed in compression to 2% and 6% strain. The compression directions are 90°, 0° and 45° with respect to the twin boundaries (TBs) of the almost parallel twins. The Dislocation Structures are analyzed by the two-beam diffraction imaging in a transmission electron microscope and by a Schmid factor analysis. In Structures deformed at 90° a high density of long straight Dislocation lines with both slip plane and Burgers vectors inclined to the twin plane (slip Mode I) are observed; they transmit across multiple TBs at a strain of 2% and form a high density of Dislocations on TBs at a strain of 6%. In Structures deformed at 0° Dislocations with Burgers vectors parallel to the twin plane (slip Mode II) are confined within Twin/Matrix lamellae and the analysis shows that both slip Mode I and II are active with dominance of Mode II. In Structures deformed at 45° Dislocations from slip Modes I, II and III are identified, where Mode III Dislocations consist of partial Dislocations moving along the TBs and full Dislocations inside the twin lamellae gliding on the slip planes parallel to the twin plane. The analysis of the Dislocation Structures illustrate the strong correlation between active slip systems and the Dislocation Structure and the strong effect of slip mode anisotropy on both the flow stress and strain hardening rate of nanotwinned Cu.
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Tailoring Dislocation Structures and mechanical properties of nanoStructured metals produced by plastic deformation
Scripta Materialia, 2009Co-Authors: Xiaoxu HuangAbstract:The presence of a Dislocation Structure associated with low-angle Dislocation boundaries and interior Dislocations is a common and characteristic feature in nanoStructured metals produced by plastic deformation, and plays an important role in determining both the strength and ductility of the nanoStructured metals. The Dislocation Structure can be modified by post-process annealing and deformation which points to new ways of optimizing the mechanical properties. Such ways are demonstrated and discussed.
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Dislocation Structures. Part II. Slip system dependence
Philosophical Magazine, 2007Co-Authors: Grethe Winther, Xiaoxu HuangAbstract:Part I established, via extensive transmission electron microscopy investigations, that the type of Dislocation Structure formed in metals of medium-to-high stacking fault energy upon deformation in tension or rolling to moderate strain levels (≤0.8) depends strongly on crystallographic grain orientation. This paper analyzes the grain orientation-dependent Structures in terms of the active slip systems, focusing on the crystallographic plane of extended planar boundaries (geometrically necessary boundaries). The analysis establishes slip systems as the factor controlling the Dislocation Structure. Five fundamental slip classes, consisting of one to three active slip systems, have been identified. Multiple activation of these slip classes is also considered. The slip classes give rise to different types of Dislocation Structure, of which all except one contains geometrically necessary planar boundaries aligning with unique crystallographic planes (not necessarily slip planes). A slip class leads to the sam...
Cristian Teodosiu - One of the best experts on this subject based on the ideXlab platform.
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prediction of forming limit strains under strain path changes application of an anisotropic model based on texture and Dislocation Structure
International Journal of Plasticity, 1998Co-Authors: Shunji Hiwatashi, Albert Van Bael, Paul Van Houtte, Cristian TeodosiuAbstract:Abstract Strain-path changes strongly influence the forming limit strains of sheet metals. The value of the limit strains is greatly affected by material-related effects such as initial anisotropy, transient. hardening, Bauschinger effect and cross hardening. A model which can describe these mechanical behaviours has been developed on the physical basis of texture and Dislocation Structure, and applied in conjunction with the Marciniak-Kuczynski analysis of the forming limit strains. The results are represented in forming limit diagrams (FLDs) in which the forming limit strains are indicated. The calculation successfully predicts some of the experimental tendencies which cannot be reproduced by conventional phenomenological models. Furthermore, the model has been used to discuss the effects of texture and Dislocation Structure on the FLDs. Especially, it is suggested that transient hardening caused by the latent part of the persistent Dislocation Structure significantly reduces the forming limit strain for a strain-path change from equi-biaxial stretching to uniaxial tension.
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Modelling of plastic anisotropy based on texture and Dislocation Structure
Computational Materials Science, 1997Co-Authors: Shunji Hiwatashi, Albert Van Bael, Paul Van Houtte, Cristian TeodosiuAbstract:Abstract Anisotropy and work hardening behaviour are the most significant material properties in sheet metal forming. Beside the initial anisotropy due to crystallographic texture, anisotropic hardening due to the evolution of the Dislocation Structure is observed at large prestrains. The developed model is a mixed hardening model in which the shape of the yield locus is generated from the texture and the Dislocation Structures are responsible for isotropic hardening and kinematic hardening. This microstructural evolution is modelled with three internal state variables and their evolution equations. Furthermore an elastoplastic tangent modulus is derived from the plasticity model. The model is constructed in the framework of dual potentials both in deviatoric stress space and plastic strain rate space. Finally, the flow stress evolution is computed for several strain-path changes.
János Lendvai - One of the best experts on this subject based on the ideXlab platform.
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Characterization of self-similar Dislocation Structures by X-ray diffraction
Materials Science and Engineering: A, 2002Co-Authors: F Székely, István Groma, János LendvaiAbstract:The development of the statistical parameters of the Dislocation Structure during plastic deformation of copper single crystals (average Dislocation density, and average Dislocation density fluctuation) was investigated by the method of X-ray diffraction peak profile analysis. It is found that during the deformation process, while the Dislocation density increases monotonically, the average fluctuation exhibits a maximum corresponding to the transition from stage II to stage III of work hardening. The fractal dimension of the Dislocation Structure was also investigated. A strong correlation was found between the fractal dimension and the relative Dislocation density fluctuation.
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Statistic properties of Dislocation Structures investigated by X-ray diffraction
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2001Co-Authors: F Székely, István Groma, János LendvaiAbstract:The method of X-ray line profile analysis was applied to obtain statistical parameters (average Dislocation density, net Dislocation polarization and average Dislocation density fluctuation) of the Dislocation Structure developed in copper single crystals deformed in uniaxial compression. It is found that during the plastic deformation, while the Dislocation density increases monotonously, the average fluctuation has a maximum at the transition from stage II to stage III work hardening. The fractal properties of the Dislocation Structure are also investigated. Strong correlation was found between the fractal dimension and the relative Dislocation density fluctuation.
Niels Hansen - One of the best experts on this subject based on the ideXlab platform.
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dependence of Dislocation Structure on orientation and slip systems in highly oriented nanotwinned cu
Acta Materialia, 2017Co-Authors: Qiuhong Lu, Niels Hansen, Xiaoxu Huang, L LuAbstract:Abstract To explore the correlation between orientation, active slip systems and Dislocation Structure, highly oriented nanotwinned Cu has been deformed in compression to 2% and 6% strain. The compression directions are 90°, 0° and 45° with respect to the twin boundaries (TBs) of the almost parallel twins. The Dislocation Structures are analyzed by the two-beam diffraction imaging in a transmission electron microscope and by a Schmid factor analysis. In Structures deformed at 90° a high density of long straight Dislocation lines with both slip plane and Burgers vectors inclined to the twin plane (slip Mode I) are observed; they transmit across multiple TBs at a strain of 2% and form a high density of Dislocations on TBs at a strain of 6%. In Structures deformed at 0° Dislocations with Burgers vectors parallel to the twin plane (slip Mode II) are confined within Twin/Matrix lamellae and the analysis shows that both slip Mode I and II are active with dominance of Mode II. In Structures deformed at 45° Dislocations from slip Modes I, II and III are identified, where Mode III Dislocations consist of partial Dislocations moving along the TBs and full Dislocations inside the twin lamellae gliding on the slip planes parallel to the twin plane. The analysis of the Dislocation Structures illustrate the strong correlation between active slip systems and the Dislocation Structure and the strong effect of slip mode anisotropy on both the flow stress and strain hardening rate of nanotwinned Cu.
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Anisotropy in rolled metals induced by Dislocation Structure
Acta Materialia, 2006Co-Authors: Grethe Winther, Niels HansenAbstract:The flow stress anisotropy of rolled sheets of aluminium, copper and interstitial-free steel has been investigated by tensile testing. Strong anisotropy, i.e., larger than expected from the texture, was induced by the Dislocation Structure in aluminium and IF steel increasing with the rolling prestrain while no such effect was found in copper. Taking into account the different spacings, misorientations and crystallographic alignment of the Dislocation boundaries as well as the texture induced by rolling in the three metals, the anisotropy was modelled as arising from the resistance to slip offered by parallel Dislocation boundaries. Good agreement between prediction and experiment also concerning the absolute flow stress values was found for all three metals. The best agreement was for aluminium, where the Dislocation Structure has been most thoroughly characterized.
Shunji Hiwatashi - One of the best experts on this subject based on the ideXlab platform.
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prediction of forming limit strains under strain path changes application of an anisotropic model based on texture and Dislocation Structure
International Journal of Plasticity, 1998Co-Authors: Shunji Hiwatashi, Albert Van Bael, Paul Van Houtte, Cristian TeodosiuAbstract:Abstract Strain-path changes strongly influence the forming limit strains of sheet metals. The value of the limit strains is greatly affected by material-related effects such as initial anisotropy, transient. hardening, Bauschinger effect and cross hardening. A model which can describe these mechanical behaviours has been developed on the physical basis of texture and Dislocation Structure, and applied in conjunction with the Marciniak-Kuczynski analysis of the forming limit strains. The results are represented in forming limit diagrams (FLDs) in which the forming limit strains are indicated. The calculation successfully predicts some of the experimental tendencies which cannot be reproduced by conventional phenomenological models. Furthermore, the model has been used to discuss the effects of texture and Dislocation Structure on the FLDs. Especially, it is suggested that transient hardening caused by the latent part of the persistent Dislocation Structure significantly reduces the forming limit strain for a strain-path change from equi-biaxial stretching to uniaxial tension.
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Modelling of plastic anisotropy based on texture and Dislocation Structure
Computational Materials Science, 1997Co-Authors: Shunji Hiwatashi, Albert Van Bael, Paul Van Houtte, Cristian TeodosiuAbstract:Abstract Anisotropy and work hardening behaviour are the most significant material properties in sheet metal forming. Beside the initial anisotropy due to crystallographic texture, anisotropic hardening due to the evolution of the Dislocation Structure is observed at large prestrains. The developed model is a mixed hardening model in which the shape of the yield locus is generated from the texture and the Dislocation Structures are responsible for isotropic hardening and kinematic hardening. This microstructural evolution is modelled with three internal state variables and their evolution equations. Furthermore an elastoplastic tangent modulus is derived from the plasticity model. The model is constructed in the framework of dual potentials both in deviatoric stress space and plastic strain rate space. Finally, the flow stress evolution is computed for several strain-path changes.