Impact of anisotropy and viscosity to model the mechanical behavior of Ti-6A1-4V alloy

This paper compares the predictions of an isotropic-thermo-elasto-viscoplastic approach and of an anisotropic-thermo-elastoplastic one with experimental results representative of the mechanical behavior of Ti-6Al-4V at moderate temperatures and low strain rates. The first model is the well known Norton-Hoff viscoplastic constitutive law with isotropic von Mises yield locus identified by using monotonic tension tests performed at strain rates from 10-3 s-1 to 10-1 s-1 and at temperatures up to 400°C. The second model is a thermo-elasto-plastic one defined by the orthotropic yield criterion CPB06. It takes into account the anisotropy and the strength differential (SD) effect in tension-compression of Ti-6Al-4V at RT, 150°C and 400°C. The identification of the SD effect is done by using tension and compression tests and the anisotropy behavior is identified by using shear, plane strain, tension and compression tests performed in three orthogonal material directions. The accuracy of the load and displacements predictions of the two macroscopic constitutive models are compared to experimental results obtained from tests performed on specimens with multiaxial loadings and large strain at several temperatures

On the evaluation of the through thickness residual stresses distribution of cold formed profiles

peer reviewedThe aim of this research is to evaluate the through thickness residual stresses distribution in the walls and in the corners of a cold-formed open section made of a material presenting a non linear hardening behaviour. To get results as close as possible to the reality, the complete process is modeled, including coiling and uncoiling of the sheet before the cold bending of the corner itself. The elastic springback after flattening as well as after final shaping are also taken into account. In order to validate the model in predicting the residual stresses distribution, the presented results are confronted to experimental measurements and FE results collected from the literature

Bauschinger effect in thin metallic films by fem simulations

Unpassivated free-standing gold and aluminum thin films (thickness ~ 200-400 nm, mean grain size dm,Au≈ 70-80nm, dm,Al≈ 120-200nm), subjected to tensile tests show Bauschinger effect (BE) during unloading [1, 2]. The focus of this work is to investigate the effect of microstructural heterogeneity such as grain sizes on the BE and the macroscopic deformation behavior in thin metallic films. The finite element code LAGAMINE is used to model the response of films involving sets of grains with different strengths. The numerical results are compared with experimental results from tensile tests on aluminum thin films from the work of Rajagopalan, et al. [2]

On Damage Characterization of a Steel Sheet

Ductile damage is a physical phenomena which involves progressive deterioration of mechanical properties of metals, when undergoing high deformations. Compared to plasticity, the physical mechanisms behind damage are more complex and the microscale is not longer negligible. In mathematical damage models, founding an optimal set of material parameters can be a hard task due to the strong coupling and non-linearity of the equations. An identification strategy is then crucial to arrive to a general set of parameters. Therefore, we address the fully characterization of a ferritic steel sheet, involving the elasto-plastic and damage parameters. This poster presents an hybrid experimental-numerical procedure, coupling numerical simulations, optimization algorithms and digital image correlation measurements, over a set of representative experimental and numerical results of tensile, shear and plane strain tests in different material directions. Due to the small thickness of the sheet, the constitutive model is very prone to localization into a shear band difficulting the damage parameters identification. It is found that a porosity induced inhomogeneity plus a mixed hardening can delay localization and represent the entire deformation range of the tests, leading to acceptable results. Different set of parameters are also obtained and then validated with experimental results. This localization phenomena should be carefully considered in applications involving complex strain paths

Developments in finite element simulations of continuous casting

peer reviewedTwo complementary approaches of steel continuous casting modelling using the finite element code LAGAMINE have been developed in the M&S Department. We propose here a description of the context in which the study started, then a description of both macroscopic and mesoscopic approaches. The first one describes the whole continuous casting process, from the free surface in the mould and through the entire machine, including thermal and mechanical behaviour of the steel. The second approach focuses on the prediction of cracks and is developed at the grain scale. Some results are also presented for both models

Developments in finite element simulations of continuous casting

peer reviewedTwo complementary approaches of steel continuous casting modelling using the finite element code LAGAMINE have been developed in the M&S Department. We propose here a description of the context in which the study started, then a description of both macroscopic and mesoscopic approaches. The first one describes the whole continuous casting process, from the free surface in the mould and through the entire machine, including thermal and mechanical behaviour of the steel. The second approach focuses on the prediction of cracks and is developed at the grain scale. Some results are also presented for both models

Texture evolution during deep-drawing processes

peer reviewedThis paper presents a constitutive law based on Taylor’s model implemented in our non-linear finite element code LAGAMINE. The yield locus is only locally described and a particular interpolation method has been developed. This local yield locus model uses a discrete representation of the material’s texture. The interpolation method is presented and a deep-drawing application is simulated in order to show up the influence of the texture evolution during forming processes

Correcting tensile test results of ECAE-deformed aluminium

Performing tensile tests on ECAE material reveals a long post-uniform elongation. In order to calculate correct true stress–true strain diagrams, three different approaches are used: measurements of the actual sample geometry, a neck evolution model proposed by Segal [V.M. Segal, S Ferrasse, F. Alford, Mater. Sci. Eng. A442 (2006) 321–326] and an inverse modelling method by finite element (FE) simulations

Assessment of the enhanced assumed strain (eas) and the assumed natural strain (ans) techniques in the mechanical behavior of the SSH3D solid-shell element

This paper presents the recently developed SSH3D Solid-Shell element implemented in the home-made LAGAMINE finite element code. This element is based on the Enhanced Assumed Strain (EAS) technique and the Assumed Natural Strain (ANS) technique. These techniques permit to avoid locking problems even in very bad conditions (nearly incompressible materials, very thin elements conducting to large aspect ratios, distorted element geometry…). The EAS technique artificially introduces additional degrees of freedom (DOFs) to the element. In the current configuration of the SSH3D element, up to 30 independent DOFs can be added to the 24 classical displacement DOFs (corresponding to the 3 displacements of the 8 element nodes). Contrarily to the nodal displacements, these additional DOFs are not linked between adjacent elements, so that they can be eliminated at the element level during the computation of the solution (before the assembling procedure). Nevertheless, they permit to increase the flexibility of the element which is very efficient for several locking issues. On the other hand, the ANS technique modifies the interpolation scheme for particular strain components. This technique is useful when shear and curvature locking problems are encountered. The ANS technique proved to eliminate the transverse shear locking from the element in bending dominated situations. In the current configuration of the element, four different versions of the ANS technique were implemented in the SSH3D element. Besides, a numerical integration scheme dedicated to Solid-Shell elements was implemented. It uses a user-defined number of integration points along the thickness direction, which permits to increase the element accuracy with a mesh containing a reduced number of elements along the thickness direction. In Sections 2, 3 and 4, the main features of the SSH3D element, i.e. the EAS technique, the ANS technique and the integration scheme are briefly described. Then, in this study, the quality of the element results is assessed in different applications. The effects of the EAS technique and the integration scheme on the volumetric locking and the effects of the ANS technique on the bending behavior of the element are analyzed in Sections 5 and 6

Thermo-mechanical-metallurgical model to predict geometrical distortions of rings during cooling phase after ring rolling operations

peer reviewedThe paper presents a validated numerical model able to predict geometrical distortions of rings during cooling phase after hot ring rolling operations. The model is capable to take into account the effects of all the phenomena resulting from the coupling of thermal, mechanical and metallurgical events. As simulation results strongly depend on the accuracy of input data, physical simulation experiments on real-material samples are developed and carried out to characterize material behaviour during phase transformation. The numerical model is then validated by an industrial case proving its effectiveness in predicting final ring distortions at room temperature