A mechanical behavior law for the numerical simulation of the mushy zone in welding

The aim of this work is to propose a mechanical behavior law dedicated to the mushy zone located between the solid phase and the weld pool in welding. The objective is to take into account of the influence of the mushy zone in the simulation of welding in order to improve the computation of induced effects such as residual stresses

Simulation of material consequences induced by fsw for a trigonal pin

The numerical simulation of Friction Stir Welding processes involves the coupling of a solid mechanics approach under large strains and large strain rates and heat transfer. The eulerian formalism leads to specially efficient finite element simulations of the matter flow under steady conditions. But with such a formulation, the calculation of the consequences induced by the stirring on the material (stirred state, microstructure, etc.) requires the coupling of advection equations for integrating the associated state variables. In this paper, a moving mesh strategy is proposed for the numerical simulation of Friction Stir Welding and material consequences, for complex pin’s geometries. The numerical processing is detailed and the efficiency of the proposed method is discussed on a Friction Stir Welding simulation of 7075 series aluminum alloy

In-plane/out-of-plane separated representations of updated Lagrangian descriptions of viscoplastic flow models in plate domains

A new efficient updated Lagrangian strategy for numerical simulations of material forming processes is presented. The basic ingredient is the tensorial decomposition of the velocity field into a finite sum of in-plane and an out-of-plane components, giving rise to an equivalent computational complexity of some two-dimensional problems and some one-dimensional ones (therefore, much less than the true three-dimensional complexity of the original problem). This is efficiently achieved by using Proper Generalized Decomposition (PGD) techniques, which are here employed in an updated Lagrangian framework for the very first time. This updated Lagrangian nature of the method needs the use of a robust numerical integration technique (in this case, the Stabilized Conforming Nodal Integration has been chosen) for addressing the highly distorted projected meshes. The resulting strategy is of general purpose, although it is especially well suited for addressing models defined in plate or shell (in general, parallelepipedic) domains. The basics of the just-developed method are shown, together with some numerical examples to show the potential of the technique

Application of the proper generalized decomposition to elasto-plastic finite element analysis

The aim of this paper is to develop the PGD for time dependent elastoplastic problems with cyclic loadings. The objective is to show that the PGD can be well suited for simulating a ratchet effect by separating space and time, and using a finite element approximation for both variables. The first part of this paper is dedicated to the mechanical formulation of the problem and especially the nonlinear behavior of the material. Then, the PGD approximation and the finite element discretization are presented, as well as the computational strategy. Finally, two examples are presented to show the capability of the method

Recent advances in residual stress simulation caused by the welding process

The purpose of the present paper is to improve the description of residual stress field characteristics generated after welding. The behavior of the material both in the liquidand solid states and during all heating and cooling stages including the solidification in the mushy zone is considered, as well as the surface tension effects in the liquid phase.Simulations are conducted on the finite element software SYSWELD®. A displacement/pressure mixed formulation, based on the linear tetrahedral element of type P1/P1 in the context of elasto-viscoplastic formulation, is used. As regards the structure behaviour,thecontinuous transition between the liquid and the solid phases during the welding is ensured using a mixture law behavior. Numerical simulations were carried out in the context of Lagrangian approach. In this approach the material over the liquidus temperature is modelled as a Newtonian fluid but the flows in the weld pool are not accounted for.Concerning surface tension modelling,the standard method usually adoptedis to apply an externalloadon the freesurface of the weld pool. In the present study, a surfacespherical stress state is directly imposed on the surface in membrane elements incorporated in the meshand representing the interface.Since tetrahedral mesh is easily adapted to complex geometry, a discretization of type P1/P1 is used in the case of welding simulation. It shows the relevance of such tetrahedral finite element for the mechanical analysis of elasto-viscoplastic solid metal.A representative simulation of a laser welding case is processed. The material considered in H. Sallem, E.Feulvarch, H.Amin El Sayed, B.Souloumiac, J-B Leblond, J-M Bergheau this study is the Inconel 600 alloy. Computed residual stress distribution revealsthe ability of such approaches topredictresidual stress states in assessing the integrity of welded components

Fast 3D simulation of a single-pass steel girth weld

The prediction of welding residual stresses requires accurate account to be taken of the couplings between heat transfer, metallurgy and stresses-strains in the heat affected zone. To begin with, simulations of residual stresses for welding processes were performed at the beginning of the 1970s. Since then, calculations have been compared and validated with experimental measurements, the major problem remaining is the calculation time. Despite the technological evolution of computers, a 3D calculation can last several days. To avoid this difficulty, a 3D simplified approach is proposed in this article. It consists of decreasing the computation time for the current zone of the welds. To show the relevance of such an approach, the methodology developed is presented through the application of a single-pass steel girth weld. For this application, the computing time can be reduced by more than 67% compared to a standard “step by step” simulation

Simulation of material consequences induced by fsw for a trigonal pin

The numerical simulation of Friction Stir Welding processes involves the coupling of a solid mechanics approach under large strains and large strain rates and heat transfer. The eulerian formalism leads to specially efficient finite element simulations of the matter flow under steady conditions. But with such a formulation, the calculation of the consequences induced by the stirring on the material (stirred state, microstructure, etc.) requires the coupling of advection equations for integrating the associated state variables. In this paper, a moving mesh strategy is proposed for the numerical simulation of Friction Stir Welding and material consequences, for complex pin’s geometries. The numerical processing is detailed and the efficiency of the proposed method is discussed on a Friction Stir Welding simulation of 7075 series aluminum alloy

Analyse de l’écaillage et de la déchromisation a l’interface oxyde/alliage modèle Ni-16Cr-9Fe

Les alliages base nickel-chrome sont connus pour être résistants à l’oxydation à haute température : l’oxydation de ces alliages engendre la formation d’une couche riche en chrome qui est communément considérée comme protectrice. Une des conséquences majeures de la croissance de ce type d’oxyde est un appauvrissement en chrome à proximité de l’interface oxyde/alliage. Ce phénomène a été étudié sur un alliage modèle Ni-16Cr-9Fe oxydé à 950 °C durant 10 h. Des analyses MEB/EDX sur coupe transverse permettent d’obtenir le profil de concentration en chrome dans l’alliage jusqu’à une distance de 1,2 μm de l’interface. Néanmoins, ces analyses sont insuffisantes pour accéder à la teneur en chrome à l’interface oxyde/alliage. Des analyses de surface par spectrométrie d’électrons Auger couplée à de l’abrasion ionique ont été réalisées à partir de l’interface oxyde/alliage jusqu’à une profondeur de 1,5 μm, ceci afin d’obtenir le profil de concentration en chrome avec une résolution nanométrique. Finalement, nous obtenons un profil complet de déchromisation avec une concentration en chrome à l’interface qui est inférieure à 1 % massique