Finite element modeling of superplastic sheet forming processes. Identification of rheological and tribological parameters by inverse method

International audienceSuperplastic forming is a thermoforming-like process commonly applied to titanium and aluminum alloys at high temperature and in specific conditions. This paper presents the application of an inverse analysis technique to the identification of theological and tribological parameters. The method consists of two steps. First, two different kinds of forming tests have been carried out for rheological and tribological identification, using specific mold shapes. Accurate instrumentation and measurements have been done in order to feed an experimental database (values of appropriate observables). In a second step, the development of an inverse method has been carried out. It consists of the minimization of an objective function representative of the distance - in a least squares sense - between measured and calculated values of the observables. The algorithm, which is coupled with the finite element model FORGE2(R), is based on a Gauss-Newton method, including a sensitivity matrix calculated by the semi-analytical metho

A coupled approach for the modelling of arc welding processes

International audienceA 3D finite element model is presented, addressing some major phenomena arising in arc welding as well as their interaction: heat input, metal deposit, solidification, phase transformations in the solid state and material behavior. As a result of a simulation, the shape of the weld bead, the phase distribution, residual stresses and distortions are obtained. Some application and validation cases are discussed

Adaptive mesh technique for thermal-metallurgical numerical simulation of arc welding processes

International audienceA major problem arising in finite element analysis of welding is the long computer times required for a complete three-dimensional analysis. In this study, an adaptative strategy for coupled thermometallurgical analysis of welding is proposed and applied in order to provide accurate results in a minimum computer time. The anisotropic adaptation procedure is controlled by a directional error estimator based on local interpolation error and recovery of the second derivatives of different fields involved in the finite element calculation. The methodology is applied to the simulation of a gas-tungsten-arc fusion line processed on a steel plate. The temperature field and the phase distributions during the welding process are analyzed by the FEM method showing the benefits of dynamic mesh adaptation. A significant increase in accuracy is obtained with a reduced computational effort

A metallurgical approach to individually assess the rheology of alpha and beta phases of Ti-6Al-4V in the two-phase domain

International audienceAn original hot torsion procedure is presented using Ti-6Al-4V in the two-phase domain. Kinetics of phase transformation are used to obtain stress-strain curves in off-equilibrium states. The individual influences of phase fraction and of temperature are quantitatively assessed in the two-phase domain. Between the two forging temperatures 1143 K (870 C) and 1228 K (955 C), a 95 MPa stress difference is observed. The paper shows that this flow stress drop is mainly due to thermal activation, by 80 MPa, while 15 MPa is due to the change of phase fraction. The stresses in each phase are individually assessed and stress-strain curves for each phase are obtained within the two-phase domai

Numerical simulation of thin sheet forming processes by the finite element method

International audienceA numerical model for solving either elastic‐plastic, elastic‐viscoplastic or purely viscoplastic deformation of thin sheets is presented, using a membrane mechanical approach. The finite element method is used associated with an incremental procedure. The mechanical equations are the principle of virtual work written in terms of plane stress, which is solved at the end of each increment, and an incremental semi‐implicit flow rule obtained by the time integration of the constitutive equations over the increment. These equations are written using curvilinear coordinates, and membrane elements are used to discretize them. The resolution method is the Newton‐Raphson algorithm. The contact algorithm is presented and allows for applications to cold stretching and deep‐drawing problems and to the superplastic forming of thin sheets

Les nouveaux défis du calcul économique

La loi a instauré l’obligation d’une évaluation socioéconomique pour tout projet d’investissement bénéficiant d’un financement de l’État ou de ses établissements publics. Elle a de plus institué des contre-expertises de ces évaluations pour les projets les plus importants. Dans ce contexte, France stratégie, le Commissariat général à l’investissement (CGI) et le Conseil général de l’environnement et du développement durable (CGEDD) ont organisé de septembre 2014 à avril 2016 une série de quatre colloques sur l’évaluation socioéconomique des projets d’investissement. Ces quatre rencontres qui ont réuni théoriciens et praticiens, experts et responsables ont largement contribué à vulgariser et diffuser la culture du calcul socioéconomique, mais surtout fait apparaître, par la discussion et le débat, des dimensions qui n’ont pas été suffisamment considérées jusqu’à présent dans les évaluations

Les nouveaux défis du calcul économique

La loi a instauré l’obligation d’une évaluation socioéconomique pour tout projet d’investissement bénéficiant d’un financement de l’État ou de ses établissements publics. Elle a de plus institué des contre-expertises de ces évaluations pour les projets les plus importants. Dans ce contexte, France stratégie, le Commissariat général à l’investissement (CGI) et le Conseil général de l’environnement et du développement durable (CGEDD) ont organisé de septembre 2014 à avril 2016 une série de quatre colloques sur l’évaluation socioéconomique des projets d’investissement. Ces quatre rencontres qui ont réuni théoriciens et praticiens, experts et responsables ont largement contribué à vulgariser et diffuser la culture du calcul socioéconomique, mais surtout fait apparaître, par la discussion et le débat, des dimensions qui n’ont pas été suffisamment considérées jusqu’à présent dans les évaluations