Mechanical behavior of low carbon steel subjected to strain path changes: Experiments and modeling (original) (raw)
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International Journal of Plasticity, 2013
Polycrystal aggregates subjected to plastic forming exhibit large changes in the yield stress and extended transients in the flow stress follow ing strain path changes. Since these effects are related to the rearrange ment of the dislocation structure induced during previous loading, here we propose a crystallographically-based dislocatio n hardening model for capturing such behavior. The model is implemented in the polycrystal code VPSC and is applied to simulate strain path changes in low carbon steel. The path changes consist of tension followed by shear at different angles with respect to the preload direction, and forward simple shear followed by reverse shear. The results are compared to experimental data and highlight the role that directional dislocation structures induced during preload play during the reload stage.
Journal of the Mechanics and Physics of Solids, 2019
This paper presents a microstructural cell-level crystal plasticity model aimed at predicting elasto-plastic, anisotropic, rate-and temperature-sensitive deformation of polycrystalline aggregates subjected to large plastic strains. The crystallography-based model embeds strain-path aware dislocation-based hardening and slip-system-level kinematic backstress laws. The crystal-level response is linked to the microstructural cell-level response using an elasto-viscoplastic fast Fourier transform-based (EVPFFT) micromechanical homogenization. The overall model is ported on a high-performance computational platform integrating a graphics processing unit (GPU) to facilitate computationally efficient modeling of high-resolution microstructures. The high-performance multi-level EVPFFT is applied to modeling monotonic and cyclic deformation of dual-phase (DP) steel sheets. To this end, the effective elastic and flow stress behavior under monotonic and cyclic deformation is calculated for several steels: three DP, DP 590, DP 980, and DP 1180, and one martensitic (MS), MS 1700. Crystallographic textures and phase fractions of these steels are characterized using electron microscopy along with electron-backscattered diffraction to initialize the models. A comprehensive set of Young's modulus, Poisson's ratio, and flow stress data is used to calibrate and validate the model. The model parameters for ferrite and martensite are identified using data for two steels and used to predict the behavior of the other two streels. The model captures elasto-plastic monotonic behavior as well as the particularities pertaining to large strain cyclic deformation characteristics such as nonlinear unloading upon the load reversal, the Bauschinger effect, and changes in hardening rate during strain reversals based on evolving microstructure including the evolution of dislocation density and crystallographic grain reorientation. In addition, it offers insights into the role of back-stress and dislocation annihilation on the cyclic deformation of DP steels.
Archives of Civil and Mechanical Engineering
The mechanical behaviours of microalloyed and low-carbon steels under strain reversal were modelled based on the average dislocation density taking into account its allocation between the cell walls and cell interiors. The proposed model reflects the effects of the dislocations displacement, generation of new dislocations and their annihilation during the metal-forming processes. The back stress is assumed as one of the internal variables. The value of the initial dislocation density was calculated using two different computational methods, i.e. the first one based on the dislocation density tensor and the second one based on the strain gradient model. The proposed methods of calculating the dislocation density were subjected to a comparative analysis. For the microstructural analysis, the high-resolution electron backscatter diffraction (EBSD) microscopy was utilized. The calculation results were compared with the results of forward/reverse torsion tests. As a result, good effectiv...
Micromechanical modeling of the elastic–viscoplastic behavior of polycrystalline steels
International Journal of Plasticity, 2001
A self-consistent model developed to describe the elastic±viscoplastic behavior of heterogeneous materials is applied to low carbon steels to simulate tensile tests at various strain rates in the low temperature range. The choice of crystalline laws implemented in the model is discussed through the viscoplastic¯ow rule and several strain-hardening laws. Comparisons between three work-hardening models show that the account of dislocation annihilation improves the results on simulations at large strains. The evolution of the Lankford coecients and texture development are also successfully simulated. Some microstructural aspects of deformation such as the stored energy and the evolution of the¯ow rates are discussed. By including the dislocation density on each slip system as internal variable, intragranular heterogeneities are underscored. #
International Journal of Plasticity, 2013
Sheet metal forming processes involve multi-axial strain paths. For the numerical simulation of such processes, an appropriate constitutive model that properly describes material behavior at large strain is required. For accurate and time-effective simulations, it is crucial to use plasticity models based on physics, as material macroscopic behavior is closely related to the evolution of the associated microstructures. Accordingly, a large strain work-hardening phenomenological model that incorporates the intragranular microstructure evolution through a dislocation density approach is proposed. The model is defined by a yield criterion and hardening laws that are all grain-size dependent. The classical Hill criterion in which grainsize dependency was introduced is proposed. Hardening laws are given by a combination of kinematic and isotropic contributions that respectively take into account the evolution with strain of cell blocks formed by geometrically necessary boundaries (GNBs) and individual dislocation cells delineated by incidental dislocation boundaries within cell blocks (IDBs). On the one hand, IDBs evolution contribution is described by a modified Rauch et al. isotropic model, which is able to describe work-hardening stagnation and work-softening. On the other hand, GNBs evolution contribution is described by a grain-size dependent tensorial backstress expression proposed by Aouafi et al. [2007] to describe the plastic anisotropy and Bauschinger effect. Moreover, the proposed model aims to accurately predict steel behavior through an innovative approach by only changing few "simply measurable" microstructure data (e.g. chemical composition, grain size…). The predictive capabilities of the model are assessed for interstitial free (IF) and dual phase (DP) steels with grain sizes varying respectively in the 8-40 µm and 1-10 µm value range. Different loading paths are analyzed, namely the uniaxial tensile test, reversal simple shear and orthogonal tests.
A dislocation-based model for high temperature cyclic viscoplasticity of 9–12Cr steels
Computational Materials Science, 2014
A dislocation-based model for high temperature cyclic viscoplasticity in 9-12Cr steels is presented. This model incorporates (i) cyclic softening via decrease in overall dislocation density, loss of low angle boundary dislocations and coarsening of the microstructure and (ii) kinematic hardening via precipitate strengthening and dislocation substructure hardening. The effects of the primary microstructural variables, viz. precipitate radii, dislocation density and martensitic lath width on cyclic viscoplasticity, reveal a size effect of initial precipitate radii and volume fraction, with smaller radii and a higher density of precipitate producing a stronger material. A similar effect is also predicted for initial martensitic lath width at temperatures below 500 °C. The model is intended for microstructure sensitive design of high temperature materials and components for next generation power plant technology.
steel research international, 2020
A successful attempt to incorporate the advantages of severe plastic deformation (SPD) methods in the continuous drawing process for low‐carbon steel is demonstrated. The structural features are considered on different scale levels, using a wide range of methods. While combining shear deformation, which parallels the basis of SPD with the conventional scheme, the cyclic process of grain refinement could be reached. As a result, the plasticity becomes enhanced. At the same time, an important characteristic such as residual stress also has a positive influence on manufacturability; particularly, the existence of the compression stress after shear deformation. The peculiarity of the structure affects the behavior of both mechanical and physical properties (like density, plasticity). The application of drawing with shear (DSh) technology as based on SPD principles, the mechanical softening effect is observed, as is the healing of microvoids. Such positive affection gives the opportunity...
Acta Materialia 60 (2012) 5791–5802
We investigate the kinetics of the deformation structure evolution and its contribution to the strain hardening of a Fe–30.5Mn–2.1Al–1.2C (wt.%) steel during tensile deformation by means of transmission electron microscopy and electron channeling contrast imaging combined with electron backscatter diffraction. The alloy exhibits a superior combination of strength and ductility (ultimate tensile strength of 1.6 GPa and elongation to failure of 55%) due to the multiple-stage strain hardening. We explain this behavior in terms of dislocation substructure refinement and subsequent activation of deformation twinning. The early hardening stage is fully determined by the size of the dislocation substructure, namely, Taylor lattices, cell blocks and dislocation cells. The high carbon content in solid solution has a pronounced effect on the evolving dislocation substructure. We attribute this effect to the reduction of the dislocation cross-slip frequency by solute carbon. With increasing applied stress, the cross-slip frequency increases. This results in a gradual transition from planar (Taylor lattices) to wavy (cells, cell blocks) dislocation configurations. The size of such dislocation substructures scales inversely with the applied resolved stress. We do not observe the so-called microband-induced plasticity effect. In the present case, due to texture effects, microbanding is not favored during tensile deformation and, hence, has no effect on strain hardening.
Dislocation substructures in tensile deformed Fe-Mn-Al-C steel
Materials Letters, 2020
Microstructure of a Fe-25Mn-2Al-0.1C steel studied under uniaxial tension revealed a gradually decreasing three-stage strain hardening behavior. Early deformation microstructure comprised of dislocations configurations; like Taylor lattice and stair-rod dislocations. Deformation twinning nucleated in regions lacking homogenous dislocation substructure. Dislocations cells and fine twin bundles were observed near failure strain. The strain hardening was a concomitant effect of deformation twins and dislocation substructure, while the contribution of dislocations seems to overwhelm the contribution from twinning.