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

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

HST Scattered Light Imaging and Modeling of the Edge-on Protoplanetary Disk ESO-Hα\alpha 569

We present new HST ACS observations and detailed models for a recently discovered edge-on protoplanetary disk around ESO H$\alpha$ 569 (a low-mass T Tauri star in the Cha I star forming region). Using radiative transfer models we probe the distribution of the grains and overall shape of the disk (inclination, scale height, dust mass, flaring exponent and surface/volume density exponent) by model fitting to multiwavelength (F606W and F814W) HST observations together with a literature compiled spectral energy distribution. A new tool set was developed for finding optimal fits of MCFOST radiative transfer models using the MCMC code emcee to efficiently explore the high dimensional parameter space. It is able to self-consistently and simultaneously fit a wide variety of observables in order to place constraints on the physical properties of a given disk, while also rigorously assessing the uncertainties in those derived properties. We confirm that ESO H$\alpha$ 569 is an optically thick nearly edge-on protoplanetary disk. The shape of the disk is well described by a flared disk model with an exponentially tapered outer edge, consistent with models previously advocated on theoretical grounds and supported by millimeter interferometry. The scattered light images and spectral energy distribution are best fit by an unusually high total disk mass (gas+dust assuming a ratio of 100:1) with a disk-to-star mass ratio of 0.16.Comment: Accepted for publication in Ap

Modélisation de l'endommagement de fluage-fatigue d'un alliage de Nickel pour récepteur solaire

Un modèle élasto-visco-plastique basé sur le modèle de Chaboche a été implémenté afin de modéliser le comportement de tubes en alliage de nickel utilisés dans les centrales solaires à tour. Pour pouvoir estimer la durée de vie des tubes, un modèle d’endommagement basé sur les travaux de Lemaitre a également été intégré au code. Ce modèle comprend deux types d’endommagement qui sont cumulés : l’endommagement de fluage, dont l’évolution suit le modèle de Kachanov, et l’endommagement de fatigue dont l’évolution suit le modèle d’endommagement unifié de Lemaitre. Le modèle a été vérifié à partir de données expérimentales issues de la littérature.SOLAR PERFOR

Orbits for the Impatient: A Bayesian Rejection Sampling Method for Quickly Fitting the Orbits of Long-Period Exoplanets

We describe a Bayesian rejection sampling algorithm designed to efficiently compute posterior distributions of orbital elements for data covering short fractions of long-period exoplanet orbits. Our implementation of this method, Orbits for the Impatient (OFTI), converges up to several orders of magnitude faster than two implementations of MCMC in this regime. We illustrate the efficiency of our approach by showing that OFTI calculates accurate posteriors for all existing astrometry of the exoplanet 51 Eri b up to 100 times faster than a Metropolis-Hastings MCMC. We demonstrate the accuracy of OFTI by comparing our results for several orbiting systems with those of various MCMC implementations, finding the output posteriors to be identical within shot noise. We also describe how our algorithm was used to successfully predict the location of 51 Eri b six months in the future based on less than three months of astrometry. Finally, we apply OFTI to ten long-period exoplanets and brown dwarfs, all but one of which have been monitored over less than 3% of their orbits, producing fits to their orbits from astrometric records in the literature.Comment: 32 pages, 28 figures, Accepted to A

Impact of distortional hardening and the strength differential effect on the prediction of large deformation behavior of the Ti6Al4V alloy

peer reviewedThe ability of three plasticity models to predict the mechanical behavior of Ti6Al4V until fracture is presented. The first model is the orthotropic yield criterion CPB06 developed by Cazacu et al. (Int J Plast 22:1171–1194, 2006) with a distortional hardening, allowing for the description of material anisotropy and the strength differential effect. The second model is the anisotropic Hill’48 yield criterion with distortional hardening, describing the material anisotropy with quadratic functions but is unable to model the strength differential effect. Finally, the third model is the classical Hill’48 yield locus with isotropic hardening. Distortional hardening is modeled through five yield surfaces associated with five levels of plastic work. Each model is validated by comparing the finite element predictions with experimental results, such as the load and displacement field histories of specimens subjected to different stress triaxiality values. Tensile tests are performed on round bars with a V-notch, a through-hole, and two different radial notches; compression tests are performed on elliptical cross-section samples. The numerical results show that none of the models can perfectly predict both the measured load and the sample shape used for validation. However, the CPB06 yield criterion with distortional hardening minimizes the global error of the model predictions. The results provide a quantification of the influence of mechanical features such as hardening phenomenon, plastic anisotropy, and tension–compression asymmetry. The impact of these features on the prediction of the post-necking deformation behavior of the Ti6Al4V alloy is explored.Dommac

Assessment of the influence of creep transition and nitridation in the creep-life prediction of Incoloy 800H

Accurate prediction of creep life of materials has been for years a matter of high research interest. The engineering design of such components is often performed following standardized analytical procedures aimed to empirically correlate state variables (mainly stress and temperature) with the chosen failure criteria (e.g., buckling, time-to-1% strain, time-to-rupture, etc). However, the accuracy of the chosen model ultimately depends on the microstructural properties of the material. As such, changes in thermomechanical treatments and environmental conditions can largely affect the creep behaviour of such components, thus making inadequate the use of simplified analytical models (R. W. Swindeman and D. L. Marriot, “Criteria for design with structural materials in combined-cycle applications above 815°F”, in Journal of Engineering for Gas Turbines and Power, vol. 116, pp. 352-359, 1993). Such is the case of Incoloy 800H, a solution-annealed austenitic Fe-Ni-Cr alloy of high industrial interest as it provides a good balance between production cost and high-temperature mechanical response. Under particularly low-stress and high-temperature loadings, this alloy is reported to exhibit a diffusion-to-dislocation transitional creep. Furthermore, the subsequent large dislocation-driven tertiary creep stage undergoes a nitridation-induced hardening while exposed to high-N environments (V. Guttmann and R. Bürgel, “Creep-structural relationship in steel alloy 800H at 900-1000°C”, in Metal Science, vol. 17, pp. 549-555, 1983). In this work, the creep behaviour of the alloy is modelled using a Chaboche-type constitutive law (H. Morch et al., “Efficient temperature dependence of parameters for thermo-mechanical finite element modelling of alloy 230”, in European Journal of Mechanics / A Solids, vol.85, 2020) implemented in the MSM-team (ULiège) proprietary finite element software Lagamine. The results are later assessed with the aim of proposing a novel and efficient numerical creep micromechanics approach intended for the identification of Chaboche parameters while addressing the underlaying uncertainties that rule the creep behaviour of this alloy: diffusion-dislocation creep transition and nitridation.Development of a generic MultiScale Creep-Fatigue approach, allowing finite element simulations to predict strains and fracture of metal components at high temperature-application on two Ni-Cr alloysMSCreep9. Industry, innovation and infrastructur

Numerical simulation of a pyramid steel sheet formed by single point incremental forming using solid-shell finite elements

peer reviewedSingle Point Incremental Forming (SPIF) is an interesting manufacturing process due to its dieless nature and its increased formability compared to conventional forming processes. Nevertheless, the process suffers from large geometric deviations when compared to the original CAD profile. One particular example arises when analyzing a truncated two-slope pyramid. In this paper, a finite element simulation of this geometry is carried out using a newly implemented solid-shell element, which is based on the Enhanced Assumed Strain (EAS) and the Assumed Natural Strain (ANS) techniques. The model predicts the shape of the pyramid very well, correctly representing the springback and the through thickness shear (TTS). Besides, the effects of the finite element mesh refinement, the EAS and ANS techniques on the numerical prediction are presented. It is shown that the EAS modes included in the model have a significant influence on the accuracy of the results

Development of a 2.5D Representative Volume Element model of AlSi10Mg material produced by additive manufacturing

peer reviewe

Bringing "The Moth" to Light: A Planet-Sculpting Scenario for the HD 61005 Debris Disk

The HD 61005 debris disk ("The Moth") stands out from the growing collection of spatially resolved circumstellar disks by virtue of its unusual swept-back morphology, brightness asymmetries, and dust ring offset. Despite several suggestions for the physical mechanisms creating these features, no definitive answer has been found. In this work, we demonstrate the plausibility of a scenario in which the disk material is shaped dynamically by an eccentric, inclined planet. We present new Keck NIRC2 scattered-light angular differential imaging of the disk at 1.2-2.3 microns that further constrains its outer morphology (projected separations of 27-135 AU). We also present complementary Gemini Planet Imager 1.6 micron total intensity and polarized light detections that probe down to projected separations less than 10 AU. To test our planet-sculpting hypothesis, we employed secular perturbation theory to construct parent body and dust distributions that informed scattered-light models. We found that this method produced models with morphological and photometric features similar to those seen in the data, supporting the premise of a planet-perturbed disk. Briefly, our results indicate a disk parent body population with a semimajor axis of 40-52 AU and an interior planet with an eccentricity of at least 0.2. Many permutations of planet mass and semimajor axis are allowed, ranging from an Earth mass at 35 AU to a Jupiter mass at 5 AU.Comment: Accepted to AJ; added Figure 5 and minor text edit