Experimental and Numerical Analysis of Electrical Contact Crimping to Predict Mechanical Strength

International audienceThis work focuses on the modeling of the aeronautical electrical contact crimping process for aircraft applications. Several thousands of crimped contact can be found in an airplane or a helicopter. The crimping process has thus to be mastered precisely in order to avoid expensive repairing and dangerous configurations. Electrical crimping is a plastic deformation process of a contact (component) on a multi-strand wire. All components are highly deformed in order to impose mechanical contact and electrical continuity. The components are very small for the cases studied in this work (0.12 mm diameter wire or 1 mm diameter cylinders). The work has been divided in 3 main steps. First, material characterization is performed in order to identify behavior laws to feed numerical simulations. The challenge is to be able to deal with very small components. The second point is to build an accurate a numerical model of the crimping process. The numerical model is compared with experimental results. Validation is done comparing with both laboratory devices and real crimped assemblies. Finally mechanical strength is studied. The numerical model is used to verify the impact of components’ dimensions or crimping condition on the mechanical resistance. Numerical models are also compared to experimental data

Explicit F.E. formulation with modified linear tetrahedral elements applied to high speed forming processes

International audienceWe will adapt a recent explicit FE formulation with modified linear tetrahedral elements for high speed metal forming simulation. This formulation both enables the use of efficient adaptive non structured meshers, and tackles the locking effect in quasi-incompressible cases. We implement this formulation for the infinitesimal elastic plastic case. The anti-locking modification effect will be underlined on two 3D bench marks: an elastic compression test and an elastic-plastic bar impact test

A node-nested Galerkin multigrid method for metal forging simulation

International audienceA node-nested Galerkin multigrid method is developed to solve systems provided by mixed formulations of 3D metal forming problems. An algebraic approach is used where operators are built on node-nested coarse meshes obtained by an automatic coarsening algorithm. This blackbox multigrid preconditioner is developed within the PETSc library. It is plugged to the FORGE3® finite element software. The linear rate of convergence and the very high efficiency of the resulting multigrid solver are evaluated for large scale problems with nonlinear behaviour

Numerical modelling of laser rapid prototyping by fusion wire deposit

International audienceA finite element model has been developed to simulate an innovative laser rapid prototyping process. Several numerical developments have been implemented in order to simulate the main steps of the rapid prototyping process: injection, heating, phase change and deposit. The numerical model also takes into account different phenomena: surface tension in the liquid state, asborptivity and plasma effects during materiallaser interaction. The threedimensional model is based on the lagrangian approach used in the Forge® finite element software. The thermal model coupled with materiallaser model is compared and gives good agreements. Simulations of the rapid prototyping are compared with experimental results

An enhanced Lemaitre model formulation for materials processing damage computation

The original publication is available at www.springerlink.comInternational audienceThe Lemaitre damage model is now widely used to deal with coupled damage analyses for various mechanical applications. In this article, different extensions of the model are presented and discussed to deal with complex multiaxial configurations--such as multi-stages bulk forming processes. A specific treatment is done to account for compressive damage growth, and a stress triaxiality cut-off value is considered to avoid any damage evolution below a critical negative triaxiality. The damage potential is also modified to deal with highly ductile materials, and the plastic strain is split into a negative part and a positive part to differentiate damage growth for compressive states of stress and for tensile states of stress. Finally, an anisotropic damage approach based on the comparison between grain flow orientation and principal loading directions is defined. A combination of these extensions is achieved within a single Lemaitre formulation. Application on different examples show the robustness and accuracy of the model defined in this paper

Numerical modelling of laser rapid prototyping by fusion wire deposit

A finite element model has been developed to simulate an innovative laser rapid prototyping process. Several numerical developments have been implemented in order to simulate the main steps of the rapid prototyping process: injection, heating, phase change and deposit. The numerical model also takes into account different phenomena: surface tension in the liquid state, asborptivity and plasma effects during materiallaser interaction. The threedimensional model is based on the lagrangian approach used in the Forge® finite element software. The thermal model coupled with materiallaser model is compared and gives good agreements. Simulations of the rapid prototyping are compared with experimental results

Simulation des assemblages par déformation. Vers une approche intégrée de l'assemblage dans la phase de dimensionnement

International audienceL'augmentation de structures multimatériaux dans de nombreuses industries conduit à une utilisation de plus en plus importante des procédés d'assemblage. Nous nous intéressons ici plus particulièrement aux procédés d'assemblage ponctuels par déformations plastiques tels que les différentes familles de rivetage ou encore de clinchage. Dans l'industrie automobile par exemple, la volonté permanente d'alléger la " caisse en blanc " conduit à l'utilisation de plus en plus fréquente de métaux légers tels que les alliages d'aluminium, ou encore de tôles polymères composite. Le point de soudure, majoritairement utilisé pour l'assemblage de tôles de carrosserie, n'est alors plus adapté. Les techniques de rivetage autopoinçonneur ou encore de clinchage représentent alors des solutions idéales, alliant facilité de pose, tenue mécanique appropriée et assemblage propre (absence de fumée, de projections, de bruit, d'eau)

Modélisation numérique du laminage à pas de pèlerin de tubes ODS en vu de limiter les risques d'endommagement

National audiencePour les Réacteurs à Neutrons Rapides au sodium, les matériaux de gainage de référence pour les très forts taux de combustion sont les nuances ferritiques/martensitiques ODS. Ces matériaux présentent en effet des bonnes propriétés en fluage, en résilience et en résistance à l'oxydation. Toutefois la présence des oxydes ODS font de ces nuances des matériaux très difficiles à mettre en forme. Classiquement le tube de gainage est mis en forme à froid à partir d'une ébauche tubulaire par une succession de passes de laminage à pas de pèlerin et de traitements thermiques. Dans le cadre de cette étude la modélisation numérique du procédé de laminage dans une configuration de type HPTR a été entreprise. Le modèle prend en compte toute la complexité des phénomènes physiques, mécaniques ainsi que le modèle de comportement du matériau pour simuler les déformations élastoplastiques cycliques qui apparaissent au cours de la mise forme des tubes minces. La modélisation de la cinématique du procédé a déjà été réalisée. L'utilisation de capteurs numériques pour suivre le chemin de déformation de la matière lors du procédé permet d'estimer la nature et l'amplitude des déformations cycliques subies

Finite Element Modeling of Tube Piercing and Creation of a Crack

From the issue entitled "Proceedings of the 11th ESAFORM Conference on Material Forming, Lyon (France), 23-25 April 2008, edited by P. Boisse, F. Morestin, E. Vidal-Sallé, LaMCoS, INSA de Lyon)" - http://esaform2008.insa-lyon.fr/proceedings/MS06/p_Ch_571.pdfInternational audienceA 3D simulation of Mannesmann tube piercing is performed using the finite element software Forge 2005®. The sensitivity of the simulation results to numerical methods and physical parameters is discussed. Advanced numerical schemes and refined time discretizations are required to obtain correct descriptions of the material flow. In this study, one concentrates on the stress state and damage development before the material comes in contact with the plug. Indeed, the crack is to appear prior to the action of the plug. The description of the material behaviour is found to be a key information to predict the crack development. Predictions based on a modified Lemaitre damage law and a normalised Latham and Cockroft criterion are compared

Numerical life prediction of mechanical fatigue for hot forging tools

Issu de : ESAFORM 2009 - 12th ESAFORM Conference on material forming, Enschede, THE NETHERLANDS, 27–29 April 2009International audienceIn the forging industry, tools represent an important part in term of production and costs. Enhancing their life cycle is then a challenging issue. Several mechanical and thermal mechanisms are responsible for hot forging tools damage such as wear, thermal and mechanical fatigue. This work will be focused only on the mechanical fatigue life prediction for hot forging tools. Both experimental data analysis and numerical simulation will be discussed in this paper. The aim is to perform qualitative and quantitative indicators of mechanical fatigue. First, experimental data of fatigue tests are used to identify both plastic strain-based Manson Coffin and stress-based Basquin life laws for 2 tool steel grades. These laws are quite classical for fatigue prediction [1-4]. The half-life strain or stress amplitudes are usually used for their identification but these amplitudes are very expensive to obtain from a numerical point of view since it is well known that hot work martensitic steels present a continuous cyclic softening from the first cycle till the rupture. Therefore an important number of cycles have to be simulated to reach these mechanical parameters at half-life. For all theses reasons, an alternative methodology is used [4]. The fatigue life curves are established using the mechanical parameters that are identified from the first hysteresis loops of fatigue experiments. Comparisons are performed with the fatigue laws coming from more classical identification procedure performed at half life cycle. Good agreement is shown between experimental data and the new laws. A lower scattering is even observed in experimental results in comparison to the traditional fatigue laws. Then these new laws are introduced in the commercial software Forge® and are then applied to different industrial cases. A pretty good agreement is observed between predicted tool life and industrial value