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Frederic Barlat - One of the best experts on this subject based on the ideXlab platform.
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advanced constitutive model for repeated stress relaxation accounting for transient Mobile Dislocation density and internal stress
Mechanics of Materials, 2019Co-Authors: Anand Varma, Hariharan Krishnaswamy, Jayant Jain, Myounggyu Lee, Frederic BarlatAbstract:Abstract Repeated stress relaxation tests are used to characterize the macroscopic time dependent behavior in metals. During stress relaxation, the Mobile Dislocation density and internal stress vary continuously with time. The phenomenological models available do not provide a comprehensive mathematical framework to account for transient effects during stress relaxation accurately. An advanced stress relaxation model based on the logarithmic model is proposed in the present work to overcome the limitations of existing models. The proposed model is found to fit the experimental data of SS 316 better than the available models. The proposed model in combination with Kocks–Mecking type Dislocation density model is utilized to predict the rate of strain hardening during relaxation
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a simple model for Dislocation behavior strain and strain rate hardening evolution in deforming aluminum alloys
International Journal of Plasticity, 2002Co-Authors: Frederic Barlat, Michael V Glazov, J C Brem, D J LegeAbstract:In this work, modeling of the stress–strain behavior is carried out using a simple Dislocation model. This model uses three variables to characterize the Dislocation population: The average forest and Mobile Dislocation densities, ρf and ρm, and the average Dislocation mean free path L. However, it is shown that within reasonable assumptions, only two of these variables are independent. The mathematical form derived from this Dislocation-based model was applied to experimental stress–strain data determined at room temperature for pure aluminum, 3003-O, 2008-T4, 6022-T4, 5182-O and 5032-T4 aluminum alloy sheets. The evolution of the state variables was calculated for these materials from a single stress–strain curve. The average Dislocation mean free paths at a strain of 0.5 were compared with TEM observations of Dislocation cell sizes or inter-Dislocation spacing for specimens deformed equal biaxially with the hydraulic bulge test. A very good agreement was obtained between predictions and experiments.
Michel W. Barsoum - One of the best experts on this subject based on the ideXlab platform.
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on spherical nanoindentations kinking nonlinear elasticity of mica single crystals and their geological implications
Journal of Structural Geology, 2009Co-Authors: Sandip Basu, Aiguo Zhou, Michel W. BarsoumAbstract:In this paper, we show, using cyclic spherical nanoindentation experiments, that the deformation mechanisms in mica, including basal plane ruptures and delaminations, can be explained by invoking the presence of Mobile Dislocation walls, and incipient and regular kink bands. Our results clearly show that the energy dissipated or that was stored during the deformation of muscovite depends critically on its previous deformation history and/or the pre-existing defect concentration. Once nucleated, the Dislocation-based incipient kink bands are believed to be responsible for the nonlinear elastic deformation and hysteretic loops obtained during cyclic loading. Moreover, a model is presented to estimate the number and distribution of Dislocations and the energy consumed in their motion under the indenter. From the model, we also estimate the critical resolved shear stress for the motion of basal plane Dislocations under the indenter. The implications of this work can be extended beyond mica to understand the nonlinear hysteretic deformation in other geological formations dominated by layered minerals.
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kinking nonlinear elasticity and the deformation of magnesium
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2009Co-Authors: Aiguo Zhou, Michel W. BarsoumAbstract:Despite a large body of work devoted to understanding the deformation of polycrystalline magnesium, there are still some outstanding questions, not the least of which are the nature of its microyielding and the nature of its fully reversible, hysteretic, stress-strain curves. In this article, we provide further evidence that Mg is a kinking nonlinear solid by showing excellent agreement between the predictions of our microscale model, in which fully reversible, Dislocation-based incipient kink bands (IKBs) are the key microscale element, the experimental results obtained in our study, and, just as important, the results obtained by others. It follows that microyielding and the fully reversible hysteresis loops are most likely to be due to IKB formation, with the propensity for kinking being enhanced for coarse-grained samples up to a grain size of ≈50 μm, after which further increases in grain size have little effect. From the areas of the reversible loops, the critical resolved shear stresses (CRSSs) associated with the movement of basal plane Dislocations are obtained and are shown to scale with the maximum flow stresses at which the loops are obtained. We also make the case that, at least for low strains, strains along the c-axis can be accommodated by invoking the formation of IKBs, Mobile Dislocation walls, and kink boundaries and should be included in future modeling of the deformation of polycrystalline Mg.
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kink bands nonlinear elasticity and nanoindentations in graphite
Carbon, 2004Co-Authors: Michel W. Barsoum, Anand Murugaiah, Tan Zhen-hua, Surya R. Kalidindi, Yury GogotsiAbstract:Abstract Herein we report on the response of graphite single crystals––loaded parallel to their c -axis––to a 13.5 μm radius spherical diamond nanoindenter. Up to loads of 5 mN, corresponding to stresses of ≈0.5 GPa, fully reversible hysteresis loops are observed. At stresses >0.5 GPa, the first loops are slightly open; subsequent loops, in the same location, are fully reversible and harder than the first. Simple compression experiments on polycrystalline cylinders yielded qualitatively similar results. Our results, together with much of the literature on the mechanical properties of graphite, can be explained by invoking the formation of incipient kink bands, IKB's, that give way to Mobile Dislocation walls that, in turn, coalesce into kink boundaries with increasing stress. The IKB's are fully reversible; the Dislocation walls result in plastic deformation, and the kink boundaries explain the hardening. Since the Dislocations are confined to the basal planes, they cannot entangle and can thus move reversibly over relatively large distances resulting in the dissipation of substantial amounts (up to 100 MJ/m 3 ) of energy during each cycle. At stresses >1.5 GPa, massive pop-ins––of the order of 60 μm––are observed. Examination of the craters formed provided direct evidence for kink bands and the formation of a multitude of subgrains under the indenter. Based on this work, it is clear that graphite is a member of a larger class of solids––kinking nonlinear elastic solids––that includes the M n +1 AX n phases, layered silicates, nonlinear mesoscopic elastic solids, among others.
S V Kamat - One of the best experts on this subject based on the ideXlab platform.
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room temperature plastic flow behaviour of ti 6 8mo 4 5fe 1 5al and ti 10v 4 5fe 1 5al effect of grain size and strain rate
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2007Co-Authors: Amit Bhattacharjee, P Ghosal, A K Gogia, S Bhargava, S V KamatAbstract:Abstract The effect of β grain size and strain rate on the plastic flow behaviour of Ti–6.8Mo–4.5Fe–1.5Al (Ti metal LCB) and its equi-molybdenum DMRL alloy Ti–10V–4.5Fe–1.5Al was evaluated and compared. The 0.2% yield strength in both alloys was found to obey the Hall–Petch relation. However, σ 0 (friction stress) was higher and k y (unpinning constant or stress concentration factor) was lower for the Mo containing alloy as compared to the V containing alloy. The strain rate was also found to influence the flow behaviour of both alloys. Flow softening was observed at strain rate of 10 −2 s −1 for the Mo containing alloy at room temperature itself. However, at lower strain rates (10 −4 and 10 −5 s −1 ), there was no flow softening, although no significant work hardening was seen. The strain hardening parameter γ = d σ / σ d ɛ P was calculated to explain the tensile deformation behaviour as a function of strain rate. The effect of strain rate on the flow behaviour was explained on the basis of velocity of Mobile Dislocation, localized adiabatic heating and planar slip due to the presence of ω-phase.
C X Huang - One of the best experts on this subject based on the ideXlab platform.
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strain rate sensitivity activation volume and Mobile Dislocations exhaustion rate in nanocrystalline cu 11 1 at al alloy with low stacking fault energy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014Co-Authors: C X Huang, Qingyuan WangAbstract:Abstract The strain rate sensitivity, activation volume and exhaustion of Mobile Dislocation density in nanocrystalline (NC) Cu–11.1 at%Al alloy with low stacking fault energy were studied by strain rate jump tests and repeated stress relaxations at room temperature. It was found that in comparison with NC Cu with similar grain size, the strain rate sensitivity of NC Cu–Al alloys is much small, which might due to the low SFE and the tendency of chemical short range order formation during plastic deformation. The small physical activation volume (~20 b 3 ) was determined, which could be ascribed to the Dislocation processes mediated by grain boundaries, twin boundaries. Meanwhile, a lower exhaustion rate of Mobile Dislocation density was found, possibly due to the low stacking fault energy enhancing Dislocation storage capability, the high densities of nanotwins preserving Mobile Dislocations and a lower Dislocation velocity in concentrated alloys.
Sunghak Lee - One of the best experts on this subject based on the ideXlab platform.
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Study of Bauschinger effect of acicular ferrite and polygonal ferrite through ex-situ interrupted bending tests in API X80 linepipe steels
Scientific Reports, 2018Co-Authors: Dae Woong Kim, Seok Su Sohn, Wan-keun Kim, Ki-seok Kim, Sunghak LeeAbstract:Linepipe steels complexly consisted of low-temperature transformation microstructures of bainitic ferrite, granular bainite, and acicular ferrite (AF) as well as polygonal ferrite (PF) which individually affect the Bauschinger effect occurring during the pipe-forming. In this study, microscopic analyses of electron back-scattered diffraction (EBSD) coupled with tension-compression and interrupted bending tests were performed for verification of the Bauschinger effect of AF and PF working as major microstructures in single-phase- and two-phase-rolled API X80 steels, respectively. With respect to microstructural effects on Bauschinger effect, the reduction in Mobile Dislocation density during the flattening was smaller in the AF than in the PF. However, the Dislocation pile-up at low-angle substructures and high-angle grain boundaries was more frequently observed, thereby leading to the higher back stress and Bauschinger effect in the AF. Boundary kernel average misorientation (KAM) profile played a critical role in determining the Bauschinger effect because they were closely related with the back stress. Thus, the Bauschinger effect was higher in the single-phase-rolled steel than in the two-phase-rolled steel. The present ex-situ interrupted bending methods coupled with EBSD analyses are outstanding ones for the detailed explanation of Bauschinger effect and provide an important idea for the yield strength designs of linepipe steels.