Error estimation and accurate mapping based ALE formulation for 3D simulation of friction stir welding

Reprinted with permission from AIP Conf. Proc. May 17, 2007 -- Volume 908, pp. 185-190 MATERIALS PROCESSING AND DESIGN; Modeling, Simulation and Applications; NUMIFORM '07; Proceedings of the 9th International Conference on Numerical Methods in Industrial Forming Processes; doi:10.1063/1.2740809 Copyright 2007 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of PhysicsInternational audienceAn Arbitrary Lagrangian Eulerian (ALE) formulation is developed to simulate the different stages of the Friction Stir Welding (FSW) process with the FORGE3® F.E. software. A splitting method is utilized: a) the material velocity/pressure and temperature fields are calculated, b) the mesh velocity is derived from the domain boundary evolution and an adaptive refinement criterion provided by error estimation, c) P1 and P0 variables are remapped. Different velocity computation and remap techniques have been investigated, providing significant improvement with respect to more standard approaches. The proposed ALE formulation is applied to FSW simulation. Steady state welding, but also transient phases are simulated, showing good robustness and accuracy of the developed formulation. Friction parameters are identified for an Eulerian steady state simulation by comparison with experimental results. Void formation can be simulated. Simulations of the transient plunge and welding phases help to better understand the deposition process that occurs at the trailing edge of the probe. Flexibility and robustness of the model finally allows investigating the influence of new tooling designs on the deposition process

3D numerical simulation of the three stages of Friction Stir Welding based on friction parameters calibration

International audienceAn Arbitrary Lagrangian Eulerian (ALE) formulation was developed to simulate the different stages of the Friction Stir Welding (FSW) process with the FORGE3® F.E. software. A splitting method was utilized: a) the material velocity/pressure and temperature fields are calculated, b) the mesh velocity is derived from the domain boundary evolution and an adaptive refinement criterion provided by error estimation, c) P1 and P0 variables are remapped. The proposed ALE formulation is applied to FSW simulation. Steady state welding, but also transient phases are simulated, showing good robustness and accuracy of the developed formulation. Friction parameters are identified for an Eulerian steady state simulation by comparison with experimental results. Simulations of the transient plunge and welding phases help to better understand the deposition process that occurs at the trailing edge of the probe, and in particular possible void formation. Flexibility and robustness of the model allows investigating the influence of threads and tooling designs

ALE Formulation for the Numerical Simulation of Friction Stir Welding

http://congress.cimne.com/complas05/admin/Files/FilePaper/p50.pdfAn Arbitrary Lagrangian Eulerian approach is used to simulate the Friction Stir Process. This formulation, which has been implemented into the Forge3® FE software, uses a splitting method: 1) calculation of the material velocity/pressure fields, 2) calculation of the mesh velocity, and 3) treatment of advection terms. This latter stage consists in remapping the variables necessary to the next computation step. Transport of nodal variables is carried out relatively simply by using an upwind technique. However, remapping variables stored at integration points, as the stress field, require more complex operations. Different techniques, based on patch recovery approach, have been investigated

3D simulation of adiabatic shear bands in high speed machining

Reprinted with permission from AIP Conf. Proc May 17, 2007 Volume 908, pp. 1137-1142 MATERIALS PROCESSING AND DESIGN; Modeling, Simulation and Applications; NUMIFORM '07; Proceedings of the 9th International Conference on Numerical Methods in Industrial Forming Processes; doi:10.1063/1.2740963. Copyright 2007 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of PhysicsInternational audienceA finite element model of three-dimensional high speed machining is developed. In order to catch Adiabatic Shear Band (ASB), which is about few microns wide, the simulation uses mesh adaptation triggered by an isotropic error estimator. An enhanced version of the Zienkiewicz and Booromand REP in Patches technique is used. As ASB is a much localized phenomenon, the adaptive procedure provides highly refined meshes with strong gradients of the element size, which makes it quite difficult to produce satisfactory 3D meshes. Furthermore, high speed machining leads to very important values of strain rate, deformation and possibly to extreme mesh distortion. So, an Arbitrary Lagrangian Eulerian (ALE) method is employed. With the utilized splitting method and linear finite element interpolation, the transport of nodal variables is based on the gradient calculated in the upwind element. For variables stored at the integration points, a remapping procedure using patch recovery techniques is preferred. Finally, because of the very strong thermo-mechanical coupling taking place in ASB, several thermo-mechanical coupling schemes are studied. Explicit and fully implicit schemes are compared, showing that the second one offers a stabilizing effect and a better accuracy. All of these ingredients provide a fully automatic and process independent procedure which allows detecting and following the formation of Adiabatic Shear Band in High Speed Machining. The creation of 3D segmented chip is observed and compared to 2D reference results obtained by Baker in [1]. The influence of numerical coefficients like the mesh size is investigated. Other application to actual 3D high speed machining such as blanking is also presented

The fallacy in productivity decomposition

This paper argues that the typical practice of performing growth decompositions based on log-transformed productivity values induces fallacious conclusions: using logs may lead to an inaccurate aggregate growth rate, an inaccurate description of the microsources of aggregate growth, or both. We identify the mathematical sources of this log-induced fallacy in decomposition and analytically demonstrate the questionable reliability of log results. Using firm-level data from the French manufacturing sector during the 2009-2018 period, we empirically show that the magnitude of the log-induced distortions is substantial. Depending on the definition of accurate log measures, we find that around 60-80% of four-digit industry results are prone to mismeasurement. We further find significant correlations of this mismeasurement with commonly deployed industry characteristics, indicating, among other things, that less competitive industries are more prone to log distortions. Evidently, these correlations also a affect the validity of studies that investigate the role of industry characteristics in productivity growth

RED: a Rich Epinions Dataset for Recommender Systems

Recommender Systems require speci c datasets to evaluate their approach. They do not require the same information: descriptions of users or items or users interactions may be necessary, which is not gathered in today datasets. In this paper, we provide a dataset containing reviews from users on items, trust values between users, items category, categories hierarchy and users expertise on categories. This dataset can be used to evaluate various Recommender Systems using Collaborative Filtering, Content-Based or Trust-Based

Completeness of algebraic CPS simulations

The algebraic lambda calculus and the linear algebraic lambda calculus are two extensions of the classical lambda calculus with linear combinations of terms. They arise independently in distinct contexts: the former is a fragment of the differential lambda calculus, the latter is a candidate lambda calculus for quantum computation. They differ in the handling of application arguments and algebraic rules. The two languages can simulate each other using an algebraic extension of the well-known call-by-value and call-by-name CPS translations. These simulations are sound, in that they preserve reductions. In this paper, we prove that the simulations are actually complete, strengthening the connection between the two languages.Comment: In Proceedings DCM 2011, arXiv:1207.682

Small molecule-based photocrosslinkable fluorescent materials toward multilayered and high-resolution emissive patterning

International audiencea Solution-processable green and red-emitting fluorophores possessing photopolymerizable acrylate units have been synthesized. Photocrosslinking was successfully performed in neat thin films at room temperature under low-dose UV irradiation at 365 nm. No further curing step was necessary to achieve insoluble emissive thin films displaying high optical quality. Up to 80% of the green emitting material processed as a non-doped thin film remained after photopolymerization. Despite competitive energy transfer occurring between the excited photoinitiator and the radiative excited state of red-emitting materials, up to 40% of the initial thickness could be achieved after development. The very low RMS roughness of the green and red photocrosslinked thin films after development (RMS o 0.7 nm) allowed us to fabricate multicolored stacks again with high optical quality (RMS roughness o 1.3 nm) after two cycles of irradiation and development involving successively red and green emitters. Resolved patterns as small as 600 nm in width could be obtained upon photolithography performed under an air atmosphere. High adhesion of the photocrosslinked materials on surfaces makes the resulting emissive thin films very promising for realizing complex emissive structures on flat or bend substrates as required in multiple applications such as optical data storage, organic lasers, organic light emitting diodes or counterfeiting

Low-Input maize-based cropping systems implementing IWM match conventional maize monoculture productivity and weed control

Conventional Maize Monoculture (MM), a dominant cropping system in south-western France, is now questioned for environmental reasons (nitrate leaching, pesticide use and excessive irrigation). Three low-input Cropping Systems (CS) using diverse weeding strategies (MMLI, a low-input MM implementing ploughing, a combination of on-row spraying and in-between row cultivation and cover crops; MMCT, conservation tillage MM implementing chemical control and cover crops; Maize-MSW, maize managed similar to MMLI but rotated with soybean & wheat) were compared to a reference system (MMConv, a conventional MM with tillage and a high quantity of inputs). Potential of Infestation of weeds (PI), weed biomass and crop production of these CS were compared during the first five years after their establishment. fields were also assessed in weed-free zones hand-weeded weekly in 2014 and 2015. Weed communities did not drastically differ among CS. PI and weed biomass were higher in MMCT, especially for Echinochloa crus-galli (L.) P.Beauv. and were comparable between MMConv, MMLI and Maize-MSW. Analysis of covariance between CS and weed biomass did not reveal a significant interaction, suggesting that weed biomass affected yield similarly among the CS. Comparison between weedy and weed-free zones suggested that weeds present at maize maturity negatively affected yields to the same extent for all four CS, despite having different weed biomasses. Grain yields in MMConv (11.3 ± 1.1 t ha−1) and MMLI (10.6 ± 2.3 t ha−1) were similar and higher than in MMCT (8.2 ± 1.9 t ha−1. Similar yields, weed biomasses and PI suggest that MMLI and Maize-MSW are interesting alternatives to conventional MM in terms of weed control and maize productivity and should be transferred to farmers to test their feasibility under wider, farm-scale conditions