The Experts below are selected from a list of 129 Experts worldwide ranked by ideXlab platform
Erik Nes - One of the best experts on this subject based on the ideXlab platform.
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Sub-structure strengthening and work hardening of an ultra-fine grained aluminium–magnesium alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2007Co-Authors: O. Nijs, Bjørn Holmedal, Jesper Friis, Erik NesAbstract:Abstract The mechanical properties of an Al–Mg1 alloy, processed to obtain grain sizes in the range from less than a micrometer to relatively coarse sizes, have been investigated by tensile and compression testing. A characteristic feature of the stress–strain curves of fine-grained Al–Mg-alloys is a Sharp Yield Point followed by Luders-band elongation. The flow stress at each given strain level followed a Hall–Petch type grain size dependence. However, the slope of the Hall–Petch curve is larger at the Yield Point than at strains beyond the Yield-Point elongation. The compression testing revealed a new phenomenon, namely that the range of stage-III deformation decreased with decreasing grain size, and disappeared completely for a grain size of about 0.5 μm.
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Modelling grain boundary strengthening in ultra-fine grained aluminum alloys
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2005Co-Authors: Erik Nes, Bjørn Holmedal, E. Evangelista, Knut MarthinsenAbstract:Abstract The mechanical properties of aluminum alloys with grain sizes in the range from less than a micron (ultra-fine) to hundreds of microns have been modelled within the framework of the multi-parameter microstructural work hardening model developed by Nes and co-workers [E. Nes, Prog. Mater. Sci. 41 (1998) 129–194; K. Marthinsen, E. Nes, Mater. Sci. Technol. 17 (2001) 376–388; E. Nes, K. Marthinsen, Mater. Sci. Eng. A322 (2002) 176–193; E. Nes, K. Marthinsen, B. Holmedal, Mater. Sci. Technol. B 20 (2004) 1377–1382]. The effect of grain size on the flow stress and work hardening, including a deviation from the Hall–Petch grain size dependency for ultra-fine grain sizes, is well accounted for by the model. A characteristic feature of the stress–strain behaviour of Al–Mg-alloys and ultra-fine grained variants is a Sharp Yield Point followed by Luders-band elongation. A mechanism for such an elastic–plastic transition is suggested.
Fusahito Yoshida - One of the best experts on this subject based on the ideXlab platform.
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Yield-Point Phenomena of Ti-20V-4Al-1Sn at 1073 K and Its Constitutive Modelling
MATERIALS TRANSACTIONS, 2009Co-Authors: Xiao-song Wang, Hiroshi Hamasaki, M. Yamamura, Ryota Yamauchi, Takashi Maeda, Yoshihisa Shirai, Fusahito YoshidaAbstract:The deformation behaviour of β titanium alloy Ti-20V-4A1-1Sn sheet at 1073K was investigated by performing uniaxial tension experiments. The stress-strain curves show a Sharp Yield Point and the subsequent abrupt Yield drop followed by the strain softening. From the EBSD analysis, a crystallographic misorientation was found in grains even at an early stage of Yielding, even though the dynamic recovery had not yet taken place. To describe such a characteristic stress-strain response, a viscoplastic constitutive model is proposed that is built on the premise that the Yield Point phenomena are associated with the rapid dislocation multiplication at an early stage of Yielding.
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A plasticity model describing Yield-Point phenomena of steels and its application to FE simulation of temper rolling
International Journal of Plasticity, 2008Co-Authors: Fusahito Yoshida, Yuya Kaneda, Shigeo YamamotoAbstract:Abstract To describe the Yield-Point phenomena of steels, an extended version of the first author’s model (Yoshida, F., 2000. A constitutive model of cyclic plasticity. International Journal of Plasticity 16, 359–380) is proposed on the premise that the material behavior of Sharp Yield Point and the subsequent abrupt Yield drop result from a rapid dislocation multiplication and the stress-dependence of dislocation velocity. A specific feature of this model is that it describes well a high upper Yield Point, the rate-dependent Luders strain at the Yield plateau and the subsequent workhardening, as well as cyclic plasticity characteristics, such as the Bauschinger effect and rate-dependent ratcheting. Using this model, an FE simulation of temper rolling process is conducted in order to clarify its role for the elimination of the Yield Point of steel sheets. Particularly, the effect of upper Yield Point on the deformation characteristics in the process is discussed.
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A constitutive model of cyclic plasticity
International Journal of Plasticity, 2000Co-Authors: Fusahito YoshidaAbstract:Abstract This paper addresses a constitutive model of cyclic plasticity with special emphasis on the Yield-Point phenomena. In order to Point out the deformation characteristics of a mild steel, four types of experiments were conducted, i.e. uniaxial tension at several crosshead speeds, cyclic straining, and stress- and strain-controlled ratchetting. A viscoplastic constitutive model of cyclic plasticity is proposed on the premise that the phenomena of Sharp Yield Point and the subsequent abrupt Yield drop result from rapid dislocation multiplication and the stress-dependence of dislocation velocity. Besides, cyclic plasticity behavior, such as the Bauschinger effect, cyclic hardening/softening characteristics and ratchet-strain accumulation, is described by some kinematic and isotropic hardening rules. The cyclic stress–strain responses predicted by this model agree well with the corresponding experimental results.
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Yielding of Mild Steel after Hydrostatic Pressurization
Anisotropy and Localization of Plastic Deformation, 1991Co-Authors: Fusahito Yoshida, M. Itoh, M. OhmoriAbstract:A Sharp Yield Point of mild steel is absent or substantially reduced in specimens subjected to high hydrostatic pressure prior to tension. The effect of high hydrostatic pressurization on the Yielding behavior in the subsequent uniaxial tension is investigated by means of FEM simulation. A unit-cell model of an elastic-viscoplastic matrix with an elastic inclusion is used for the analysis. This analysis shows that the Yield stress reduces markedly, only when the matrix has a Sharp Yield Point and abrupt Yield-drop characteristics, and there exists an elastic inhomogeneity between the matrix and the inclusion.
Armand Joseph Beaudoin - One of the best experts on this subject based on the ideXlab platform.
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Dislocation Mediated Continuum Plasticity: Case Studies on Modeling Scale Dependence, Scale-Invariance, and Directionality of Sharp Yield-Point
Computational Methods for Microstructure-Property Relationships, 2010Co-Authors: Claude Fressengeas, Amit Acharya, Armand Joseph BeaudoinAbstract:Plasticity of crystalline solids is a dynamic phenomenon resulting from the motion under stress of linear crystal defects known as dislocations. Such a statement is grounded on numerous convincing observations, and it is widely accepted by the scientific community. Nevertheless, the conventional plasticity theories use macroscopic variables whose definition does not involve the notion of dislocation. This paradoxical situation arises from the enormous range covered by the length scales involved in the description of plasticity, from materials science to engineering. Itmay have seemed impossible to account for the astounding complexity of the (microscopic) dynamics of dislocation ensembles at the (macroscopic) scale of the mechanical properties of materials. Justifications offered for such a simplification usually reside in perfect disorder assumptions. Namely, plastic strain is regarded as resulting from a large number of randomly distributed elementary dislocation glide events, showing no order whatsoever at intermediate length scales. Hence, deriving the mechanical properties from the interactions of dislocations with defects simply requires averaging on any space and time domain. The existence of grain boundaries in polycrystals is of course affecting this averaging procedure, but it does not change it fundamentally.
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Directionality of Yield Point in strain-aged steels: The role of polar dislocations
Acta Materialia, 2008Co-Authors: Vincent Taupin, Claude Fressengeas, S. Varadhan, Armand Joseph BeaudoinAbstract:Abstract The directionality of the Sharp Yield Point in strain-aged steels has been investigated by modeling tension/compression and forward/reverse torsion tests separated by accelerated aging. The occurrence of a Bauschinger effect and the absence of a Yield Point after a forward straining–aging–reverse straining sequence are interpreted within the framework of a field dislocation theory coupling the evolution of statistical and polar dislocation densities with that of Point defects due to strain aging. The polar dislocation density reflects lattice incompatibility and long-range internal stresses. By assisting Yielding in reverse straining, the associated back-stress is seen as the origin of the Bauschinger effect. By also promoting dislocation unlocking, the back-stress is found to be responsible for the absence of a Yield Point in reverse straining. Polarized dislocation structures formed in forward straining in association with back-stress build up may annihilate and inverse polarization occur in reverse straining. This microstructure evolution translates into an inflexion of strain hardening after strain path reversal.
Bjørn Holmedal - One of the best experts on this subject based on the ideXlab platform.
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Sub-structure strengthening and work hardening of an ultra-fine grained aluminium–magnesium alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2007Co-Authors: O. Nijs, Bjørn Holmedal, Jesper Friis, Erik NesAbstract:Abstract The mechanical properties of an Al–Mg1 alloy, processed to obtain grain sizes in the range from less than a micrometer to relatively coarse sizes, have been investigated by tensile and compression testing. A characteristic feature of the stress–strain curves of fine-grained Al–Mg-alloys is a Sharp Yield Point followed by Luders-band elongation. The flow stress at each given strain level followed a Hall–Petch type grain size dependence. However, the slope of the Hall–Petch curve is larger at the Yield Point than at strains beyond the Yield-Point elongation. The compression testing revealed a new phenomenon, namely that the range of stage-III deformation decreased with decreasing grain size, and disappeared completely for a grain size of about 0.5 μm.
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Modelling grain boundary strengthening in ultra-fine grained aluminum alloys
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2005Co-Authors: Erik Nes, Bjørn Holmedal, E. Evangelista, Knut MarthinsenAbstract:Abstract The mechanical properties of aluminum alloys with grain sizes in the range from less than a micron (ultra-fine) to hundreds of microns have been modelled within the framework of the multi-parameter microstructural work hardening model developed by Nes and co-workers [E. Nes, Prog. Mater. Sci. 41 (1998) 129–194; K. Marthinsen, E. Nes, Mater. Sci. Technol. 17 (2001) 376–388; E. Nes, K. Marthinsen, Mater. Sci. Eng. A322 (2002) 176–193; E. Nes, K. Marthinsen, B. Holmedal, Mater. Sci. Technol. B 20 (2004) 1377–1382]. The effect of grain size on the flow stress and work hardening, including a deviation from the Hall–Petch grain size dependency for ultra-fine grain sizes, is well accounted for by the model. A characteristic feature of the stress–strain behaviour of Al–Mg-alloys and ultra-fine grained variants is a Sharp Yield Point followed by Luders-band elongation. A mechanism for such an elastic–plastic transition is suggested.
Knut Marthinsen - One of the best experts on this subject based on the ideXlab platform.
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Modelling grain boundary strengthening in ultra-fine grained aluminum alloys
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2005Co-Authors: Erik Nes, Bjørn Holmedal, E. Evangelista, Knut MarthinsenAbstract:Abstract The mechanical properties of aluminum alloys with grain sizes in the range from less than a micron (ultra-fine) to hundreds of microns have been modelled within the framework of the multi-parameter microstructural work hardening model developed by Nes and co-workers [E. Nes, Prog. Mater. Sci. 41 (1998) 129–194; K. Marthinsen, E. Nes, Mater. Sci. Technol. 17 (2001) 376–388; E. Nes, K. Marthinsen, Mater. Sci. Eng. A322 (2002) 176–193; E. Nes, K. Marthinsen, B. Holmedal, Mater. Sci. Technol. B 20 (2004) 1377–1382]. The effect of grain size on the flow stress and work hardening, including a deviation from the Hall–Petch grain size dependency for ultra-fine grain sizes, is well accounted for by the model. A characteristic feature of the stress–strain behaviour of Al–Mg-alloys and ultra-fine grained variants is a Sharp Yield Point followed by Luders-band elongation. A mechanism for such an elastic–plastic transition is suggested.