A new intermediate model for polycristalline viscoplastic deformation and texture evolution.

International audienc

Numerical study of deformation textures, yield locus, rolling components and Lankford coefficients for FCC polycrystals using the new polycrystalline φ-model

In this paper, we discuss results from the new viscoplastic non-linear intermediate ϕ-model for crystal plasticity. We used this viscoplastic ϕ-model in order to compute several properties and indicators directly connected to the formability of FCC polycrystalline metals. For instance, the yield locus, the Lankford coefficients and the typical FCC rolling texture component and their evolution during plastic deformation are computed. We also compare our results to those predicted by the tangent viscoplastic self-consistent model as well as those obtained by the upper and lower bounds (Taylor and Static). Results concerning FCC metals subjected to plane strain compression (commonly used for the approximation of the rolling process) are presented. As in the self-consistent scheme, the viscoplastic ϕ-model takes into account the strength of grains interactions. The influence of the grain interaction on predicted results is discussed. This analysis of the change in predicted results for different values of the parameter controlling the grain interaction strength (from a stiff to a more compliant interaction) shows that the results depend strongly on ϕ

Rolling texture transition in FCC metals using the viscoplastic φ -model and considering mechanical twinning

The viscoplastic Φ-model belongs to the same class of self-consistent models but it is based on a new theory without the Eshelby scheme. The Φ-model, by varying the parameter Φ, can predict a very large range of the texture components: from the lower (Φ →1) to the upper (Φ→0 ) bounds results. In this work, we adapt the Φ-model to take into account the mechanical twinning. This extended Φ-model is used to predict textures in FCC metals under plane strain compression test. We show that the deformation twinning plays an important role in the formation of brass-type texture

Mechanical characterization of thin metal sheets by a digital image correlation method

In this paper, différent applications of an optical method based on digital corrélation of images is presented. The most important characteristic of this method is that you cari draw a deformation map on the entire surface of the spécimen. This is a non-contact method that is easy to set-up since there is no spécial mounting requirements. Thus, it is a very attractive testing method for thin ductile metal sheets. We propose to analyze différent applications of this method to characterize the material mechanical response using tensile tests. These consist of measuring the clastic properties, characterizing the necking and its propagation up to failure, and the identification of the evolution of damage until rupture. We also prescrit a comparison between finite element simulations and the experimental data obtained by this method

Coupled effects of the lattice rotation definition, twinning and interaction strength on the FCC rolling texture evolution using the viscoplastic φ-model

Prediction of the rolling texture evolution in FCC metals is controlled by interaction laws, deformation mechanisms and definition of the lattice spin. The coupled effect of these three factors on the FCC rolling texture evolution is hereby analyzed using the viscoplastic -model. Without the Eshelby theory, this model yields an interaction law spanning predicted results from the upper to lower bound ones by varying a scalar weight parameter (). In this work, two definitions of the lattice spin, the mathematical analysis (MA) and the plane–strain analysis (PSA), are considered in the -model. The influence of the MA and PSA definitions on the FCC rolling texture evolution is deeply analyzed in conjunction with twinning and grain interaction strength, from a stiff to a more compliant interaction

Modeling of large plastic deformation behavior and anisotropy evolution in cold rolled bcc steels using the viscoplastic φ-model-based grain-interaction

In this paper, a micromechanical approach is used to predict the mechanical response and anisotropy evolution in BCC metals. Particularly, cold rolling textures and the corresponding yield surfaces are simulated using the newly developed viscoplastic intermediate ϕ-model. This model takes into account the grain interactions but without the Eshelby theory. In this work, we compare our results to those predicted by the upper and lower bounds (Taylor and Static) as well as those of the viscoplastic self-consistent (VPSC) model. The results are compared in terms of predicted slip activity, texture evolution and yield loci. For the simulations, we considered two cases: the restricted slip, {1 1 0}〈1 1 1〉, and the pencil glide, {1 1 0}〈1 1 1〉 + {1 1 2}〈1 1 1〉 + {1 2 3}〈1 1 1〉. In addition, we present a qualitative comparison with experimental cold rolling textures taken from the literature for several BCC metals: electrical, ferritic, Interstitial-Free (IF) and low carbon steels. Our results show that the pencil glide assumption is adequate for low carbon and IF-steels and that the restricted slip assumption is well suited for ferritic and electrical steels

Comparison between self-consistent and intermediate approaches for the simulation of large deformation polycrystal viscoplasticity

International audienc

Analysis of shear deformation by slip and twinning in low and high/medium stacking fault energy fcc metals using the φ-model

Experimental tests involving shear stresses allow material to be deformed to very high plastic strain by overcoming localization phenomena. The simple shear texture development, which is also common near the surface of rolled parts, is important to study since it is directly connected to the metal anisotropy. Crystal plasticity models are used to simulate large deformation plasticity and texture evolution. The main insufficiency of most existing models is that they are, in certain cases, unable to predict all type of experimentally observed textures as well as texture transitions. In this paper, we show that the polycrystalline φ-model can be used to compute simple shear crystallographic texture transition for face-centered cubic metals (fcc) at large strains. This model takes into account the grains interaction effects but without the Eshelby inclusion theory. Predicted results are compared to experimental shear textures for medium stacking fault energy (SFE) metals (i.e. copper) and low SFE metals (i.e. silver). We show that the φ-model is able to predict a clear shear texture transition characterizing a range of fcc metals having high/medium to low SFE. The twinning mechanism is included in the φ-model in order to improve the predicted shear textures for low SFE metals. The effect of twinning on the ideal shear texture components is shown and is consistent with experimental results from the literature