Int. Conf. on Computational Methods for Coupled Problems in Science and Engineering COUPLED PROBLEMS 2005 M. Papadrakakis, E. Oñate and B. Schrefler (Eds)  CIMNE, Barcelona, 2005 COUPLED THERMOMECHANICAL BEHAVIOUR FOR METAL CASTING FE ANALYSIS Michele Chiumenti, Carlos Agelet de Saracibar and Miguel Cervera International Center for Numerical Methods in Engineering, CIMNE ETS Ingenieros de Caminos, Canales y Puertos, Universidad Politécnica de Cataluña, UPC Campus Norte UPC, 08034 Barcelona, Spain e-mail: chiument@cimne.upc.es , agelet@cimne.upc.es , cervera@cimne.upc.es Key words: Coupled Problems, Multiphysics Problems, Thermomechanical Problems, Metal Casting, Finite Elements. Abstract. The aim of this work is to show the necessity of a coupled thermo-mechanical analysis for the simulation of foundry processes. The solution of such a problem consists of an up-to-date finite element numerical model for fully coupled thermo-mechanical systems. The formulation of the governing equations is consistently derived within a thermodynamic context. The proposed constitutive model is defined by a thermo-visco-plastic free energy function. A continuous transition between the initial fluid-like and the final solid-like behaviour of the part is modelled by considering an improved J2-thermo-viscoplastic model. Thus, an elasto-visco-plastic response suitable for solid-like behaviour degenerates into a purely viscous model according to the solid fraction function capturing the liquid-like behaviour [1-5]. A stabilization technique based on the orthogonal sub-grid scale method is introduced as a convenient framework to deal with the complex behaviour of the casting metal during the solidification process [6-11]. Within this formulation it is possible to properly deal with the incompressibility behaviour of either the casting material during the initial liquid phase or the isochoric viscoplastic strain evolution. Fractional step method arising from an operator split of the governing differential equations is considered. Within the time discrete setting, the additive operator splits lead to a product formula algorithm and to a staggered solution scheme of the coupled problem. Computational simulations show the good performance of the model. 1 INTRODUCTION. MOTIVATION AND GOALS The numerical formulation of coupled thermo-mechanical solidification processes has been one of the research topics of great interest over the last years. Also, during the last decade, a growing interest on this and related topics has been shown by many industrial companies, such as automotive and aeronautical, motivated by the need to get high-quality final products and to reduce manufacturing costs. However, and despite the enormous progress achieved in computational mechanics, the large-scale numerical simulation of these problems continues to be nowadays a very complex task. This is mainly due to the highly non-linear nature of the problem, involving non-linear constitutive behavior, liquid-solid phase-change, non-linear thermal and mechanical boundary conditions and thermo-mechanical contact interaction,