The Experts below are selected from a list of 282 Experts worldwide ranked by ideXlab platform
Irene J. Beyerlein - One of the best experts on this subject based on the ideXlab platform.
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first principles study of Crystallographic Slip modes in ω zr
Scientific Reports, 2017Co-Authors: Anil Kumar, Arul M Kumar, Irene J. BeyerleinAbstract:We use first-principles density functional theory to study the preferred modes of Slip in the high-pressure ω phase of Zr. The generalized stacking fault energy surfaces associated with shearing on nine distinct Crystallographic Slip modes in the hexagonal ω-Zr crystal are calculated, from which characteristics such as ideal shear stress, the dislocation Burgers vector, and possible accompanying atomic shuffles, are extracted. Comparison of energy barriers and ideal shear stresses suggests that the favorable modes are prismatic 〈c〉, prismatic-II $$\langle 10\bar{1}0\rangle $$ 〈 10 1 ¯ 0 〉 and pyramidal-II 〈c + a〉, which are distinct from the ground state hexagonal close packed α phase of Zr. Operation of these three modes can accommodate any deformation state. The relative preferences among the identified Slip modes are examined using a mean-field crystal plasticity model and comparing the calculated deformation texture with the measurement. Knowledge of the basic Crystallographic modes of Slip is critical to understanding and analyzing the plastic deformation behavior of ω-Zr or mixed α-ω phase-Zr.
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Grain neighbour effects on twin transmission in hexagonal close-packed materials
Nature communications, 2016Co-Authors: M. Arul Kumar, Irene J. Beyerlein, Rodney J. Mccabe, Carlos N. ToméAbstract:Materials with a hexagonal close-packed (hcp) crystal structure such as Mg, Ti and Zr are being used in the transportation, aerospace and nuclear industry, respectively. Material strength and formability are critical qualities for shaping these materials into parts and a pervasive deformation mechanism that significantly affects their formability is deformation twinning. The interaction between grain boundaries and twins has an important influence on the deformation behaviour and fracture of hcp metals. Here, statistical analysis of large data sets reveals that whether twins transmit across grain boundaries depends not only on crystallography but also strongly on the anisotropy in Crystallographic Slip. We show that increases in crystal plastic anisotropy enhance the probability of twin transmission by comparing the relative ease of twin transmission in hcp materials such as Mg, Zr and Ti.
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An analytical model for the critical shell thickness in core/shell nanowires based on Crystallographic Slip
Journal of The Mechanics and Physics of Solids, 2013Co-Authors: Caizhi Zhou, Irene J. BeyerleinAbstract:Abstract Employing crystal plasticity theory and micromechanics inclusion theory, we developed a full-strain relaxation model under isotropic assumption of materials properties to predict the dependence of the critical shell thickness (CST) for defect-free core/shell nanowires (NWs) on their growth direction. Unlike prior models, we consider three important factors in the energetic analysis (1) the self-energy of a dislocation loop in a finite domain, (2) the three-dimensional mismatch strains that develop in core/shell NWs (axial, radial and tangential directions) as a result of the finite NW geometry and the lattice mismatch between the core and shell materials, and (3) the three-dimensional plastic strains from misfit dislocations that nucleate to relax the mismatch strains. With these, the full-relaxation model is able to reveal that (i) the variation of the CST with growth direction depends on the core radius, (ii) misfit dislocations will not nucleate when the core radius falls below a critical value, (iii) the CST tends to a constant as the core radius increases, and (iv) the CST predicted by prior uniaxial-strain relaxation models is a lower bound.
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an analytical model for the critical shell thickness in core shell nanowires based on Crystallographic Slip
Journal of The Mechanics and Physics of Solids, 2013Co-Authors: Caizhi Zhou, Haijian Chu, Jian Wang, Irene J. BeyerleinAbstract:Abstract Employing crystal plasticity theory and micromechanics inclusion theory, we developed a full-strain relaxation model under isotropic assumption of materials properties to predict the dependence of the critical shell thickness (CST) for defect-free core/shell nanowires (NWs) on their growth direction. Unlike prior models, we consider three important factors in the energetic analysis (1) the self-energy of a dislocation loop in a finite domain, (2) the three-dimensional mismatch strains that develop in core/shell NWs (axial, radial and tangential directions) as a result of the finite NW geometry and the lattice mismatch between the core and shell materials, and (3) the three-dimensional plastic strains from misfit dislocations that nucleate to relax the mismatch strains. With these, the full-relaxation model is able to reveal that (i) the variation of the CST with growth direction depends on the core radius, (ii) misfit dislocations will not nucleate when the core radius falls below a critical value, (iii) the CST tends to a constant as the core radius increases, and (iv) the CST predicted by prior uniaxial-strain relaxation models is a lower bound.
Mgd Marc Geers - One of the best experts on this subject based on the ideXlab platform.
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lath martensite plasticity enabled by apparent sliding of substructure boundaries
Materials & Design, 2019Co-Authors: C. Du, Roumen Petrov, Mgd Marc Geers, Jpm Johan HoefnagelsAbstract:Abstract Lath martensite is widely present in advanced high strength steels as the key strengthening phase. Unexpectedly high ductility of lath martensite has been reported in the literature in both single-phase and multi-phase steels, however, without systematic identification of the underlying plasticity mechanisms. In this study, first, well-defined micro-tensile tests are carried out on fully martensitic steel with a clean large substructure and a variety of substructure boundary orientations with respect to the loading direction. Two deformation mechanisms of lath martensite were identified, namely, intra-lath Crystallographic Slip and apparent substructure boundary sliding, that compete with each other to carry the overall plasticity. The condition under which these two mechanisms are active has been clarified. It is found that boundary sliding is more easily activated than intra-lath Crystallographic Slip. In addition, for dual phase steel, as an example of multi-phase steels, the probability for sliding of lath martensite boundaries was estimated by boundary orientation characterization and micro-tensile tests. The results suggest that the apparent boundary sliding is also important for lath-martensite-containing multi-phase steels, which would explain prior reports in the literature of unexpectedly high local strains in the martensite regions.
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plasticity of lath martensite by sliding of substructure boundaries
Scripta Materialia, 2016Co-Authors: Chaowei C Du, Rene R Vaes, Jpm Johan Hoefnagels, Mgd Marc GeersAbstract:Well-defined uniaxial micro-tensile tests were performed on lath martensite with different types of substructure boundaries (block, sub-block and lath boundaries) tilted with respect to the loading direction. A characteristic deformation mechanism of lath martensite is hereby identified, i.e. sliding along the substructure boundaries. This boundary sliding can occur at all types of boundaries at relatively low stresses. Internal boundaries not only strengthen lath martensite, as well established in literature, but under favorable orientations also mitigate plastic deformation. The overall plastic deformation results from the competition of Crystallographic Slip with boundary sliding.
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a comparison of dislocation induced back stress formulations in strain gradient crystal plasticity
International Journal of Solids and Structures, 2006Co-Authors: C J Bayley, Wam Marcel Brekelmans, Mgd Marc GeersAbstract:Strain gradient crystal plasticity attempts to predict material size effects by taking into account geometrically necessary dislocations that are required to accommodate gradients of Crystallographic Slip. Since these dislocations have a non-zero net Burgers vector within the material, dislocation induced long range stresses result in a back stress that influences the effective driving force for Crystallographic Slip. A dislocation induced back stress formulation is proposed in which the full tensorial nature of the dislocation stress state is included in the continuum description. The significance of this proposed back stress formulation is that it intrinsically includes latent kinematic hardening from dislocations lying on all Slip systems. Using simple shearing of a semi-infinite cube oriented single crystal with either double-planar or octahedral Slip system configurations, the proposed back stress formulation is examined in detail.
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scale dependent crystal plasticity framework with dislocation density and grain boundary effects
International Journal of Solids and Structures, 2004Co-Authors: L Laurens P Evers, Wam Marcel Brekelmans, Mgd Marc GeersAbstract:The geometrically non-linear scale dependent response of polycrystal FCC metals is modelled by an enhanced crystal plasticity framework based on the evolution of several dislocation density types and their distinct physical influence on the mechanical behaviour. The isotropic hardening contribution follows from the evolution of statistically stored dislocation (SSD) densities during plastic deformation, where the determination of the Slip resistance is based on the mutual short range interactions between all dislocation types, i.e. including the geometrically necessary dislocation (GND) densities. Moreover, the GND's introduce long range interactions by means of a back-stress measure, opposite to the Slip system resolved shear stress. The grain size dependent mechanical behaviour of a limited collection of grains under plane stress loading conditions is determined using the finite element method. Each grain is subdivided into finite elements and an additional expression, coupling the GND densities to spatial Crystallographic Slip gradients, renders the GND densities to be taken as supplemental nodal degrees of freedom. Consequently, these densities can be uncoupled at the grain boundary nodes, allowing for the introduction of grain boundary dislocations (GBD's) based on the lattice mismatch between neighbouring grains and enabling the obstruction of Crystallographic Slip perpendicular to the grain boundary.
Caizhi Zhou - One of the best experts on this subject based on the ideXlab platform.
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An analytical model for the critical shell thickness in core/shell nanowires based on Crystallographic Slip
Journal of The Mechanics and Physics of Solids, 2013Co-Authors: Caizhi Zhou, Irene J. BeyerleinAbstract:Abstract Employing crystal plasticity theory and micromechanics inclusion theory, we developed a full-strain relaxation model under isotropic assumption of materials properties to predict the dependence of the critical shell thickness (CST) for defect-free core/shell nanowires (NWs) on their growth direction. Unlike prior models, we consider three important factors in the energetic analysis (1) the self-energy of a dislocation loop in a finite domain, (2) the three-dimensional mismatch strains that develop in core/shell NWs (axial, radial and tangential directions) as a result of the finite NW geometry and the lattice mismatch between the core and shell materials, and (3) the three-dimensional plastic strains from misfit dislocations that nucleate to relax the mismatch strains. With these, the full-relaxation model is able to reveal that (i) the variation of the CST with growth direction depends on the core radius, (ii) misfit dislocations will not nucleate when the core radius falls below a critical value, (iii) the CST tends to a constant as the core radius increases, and (iv) the CST predicted by prior uniaxial-strain relaxation models is a lower bound.
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an analytical model for the critical shell thickness in core shell nanowires based on Crystallographic Slip
Journal of The Mechanics and Physics of Solids, 2013Co-Authors: Caizhi Zhou, Haijian Chu, Jian Wang, Irene J. BeyerleinAbstract:Abstract Employing crystal plasticity theory and micromechanics inclusion theory, we developed a full-strain relaxation model under isotropic assumption of materials properties to predict the dependence of the critical shell thickness (CST) for defect-free core/shell nanowires (NWs) on their growth direction. Unlike prior models, we consider three important factors in the energetic analysis (1) the self-energy of a dislocation loop in a finite domain, (2) the three-dimensional mismatch strains that develop in core/shell NWs (axial, radial and tangential directions) as a result of the finite NW geometry and the lattice mismatch between the core and shell materials, and (3) the three-dimensional plastic strains from misfit dislocations that nucleate to relax the mismatch strains. With these, the full-relaxation model is able to reveal that (i) the variation of the CST with growth direction depends on the core radius, (ii) misfit dislocations will not nucleate when the core radius falls below a critical value, (iii) the CST tends to a constant as the core radius increases, and (iv) the CST predicted by prior uniaxial-strain relaxation models is a lower bound.
Haijian Chu - One of the best experts on this subject based on the ideXlab platform.
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an analytical model for the critical shell thickness in core shell nanowires based on Crystallographic Slip
Journal of The Mechanics and Physics of Solids, 2013Co-Authors: Caizhi Zhou, Haijian Chu, Jian Wang, Irene J. BeyerleinAbstract:Abstract Employing crystal plasticity theory and micromechanics inclusion theory, we developed a full-strain relaxation model under isotropic assumption of materials properties to predict the dependence of the critical shell thickness (CST) for defect-free core/shell nanowires (NWs) on their growth direction. Unlike prior models, we consider three important factors in the energetic analysis (1) the self-energy of a dislocation loop in a finite domain, (2) the three-dimensional mismatch strains that develop in core/shell NWs (axial, radial and tangential directions) as a result of the finite NW geometry and the lattice mismatch between the core and shell materials, and (3) the three-dimensional plastic strains from misfit dislocations that nucleate to relax the mismatch strains. With these, the full-relaxation model is able to reveal that (i) the variation of the CST with growth direction depends on the core radius, (ii) misfit dislocations will not nucleate when the core radius falls below a critical value, (iii) the CST tends to a constant as the core radius increases, and (iv) the CST predicted by prior uniaxial-strain relaxation models is a lower bound.
M T Perezprado - One of the best experts on this subject based on the ideXlab platform.
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analysis of Crystallographic Slip and grain boundary sliding in a ti 45al 2nb 2mn at 0 8 vol tib2 alloy by high temperature in situ mechanical testing
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014Co-Authors: R Munozmoreno, E M Ruiznavas, C J Boehlert, J Llorca, J M Torralba, M T PerezpradoAbstract:This work aims to contribute to a further understanding of the fundamentals of Crystallographic Slip and grain boundary sliding in the γ-TiAl Ti–45Al–2Nb–2Mn (at%)–0.8 vol%TiB2 intermetallic alloy, by means of in situ high-temperature tensile testing combined with electron backscatter diffraction (EBSD). Several microstructures, containing different fractions and sizes of lamellar colonies and equiaxed γ-grains, were fabricated by either centrifugal casting or powder metallurgy, followed by heat treatment at 1300 °C and furnace cooling. in situ tensile and tensile-creep experiments were performed in a scanning electron microscope (SEM) at temperatures ranging from 580 °C to 700 °C. EBSD was carried out in selected regions before and after straining. Our results suggest that, during constant strain rate tests, true twin γ/γ interfaces are the weakest barriers to dislocations and, thus, that the relevant length scale might be influenced by the distance between non-true twin boundaries. Under creep conditions both grain/colony boundary sliding (G/CBS) and Crystallographic Slip are observed to contribute to deformation. The incidence of boundary sliding is particularly high in γ grains of duplex microstructures. The Slip activity during creep deformation in different microstructures was evaluated by trace analysis. Special emphasis was placed in distinguishing the compliance of different Slip events with the Schmid law with respect to the applied stress.
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grain boundary sliding and Crystallographic Slip during superplasticity of al 5 ca 5 zn as studied by texture analysis
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 1998Co-Authors: M T Perezprado, M C Cristina, Oscar Antonio Ruano, Gaspar GonzalezdoncelAbstract:Abstract The contribution of Crystallographic Slip (CS) and grain boundary sliding (GBS) during superplastic deformation of Al–5 wt.% Ca–5 wt.% Zn at 10−2 s−1 in the temperature range of 300–550°C is discussed on the basis of texture evolution. During deformation in the transverse direction, the initial rolling texture component in the mid-layer, {225}〈554〉 (C-type), changes dramatically and the brass component, {011}〈211〉, appears. It is shown that this change is gradual and can be associated with an `equivalent' single Slip in the (111)[ 2 11] Slip system. It can be inferred from this study that both GBS and CS take place during superplastic deformation of this alloy. Quantitative evaluation of the volume fraction of crystallites (Fv) associated with texture components indicates that the testing temperature strongly influences the contribution of each of these mechanisms. The importance of GBS increases with temperature. Continuous recrystallization and (sub)grain growth, which also occur during deformation, must also be taken into consideration for a complete description of the microstructural evolution which occurs during superplastic deformation of this alloy.