Papers by Michele Chiumenti
International Journal of Material Forming, 2008
This work presents a neural networks approach for finding the effective activation energy and mod... more This work presents a neural networks approach for finding the effective activation energy and modeling the dissolution rate of hardening precipitates in aluminium alloys using inverse analysis. As way of illustration, a class of multilayer perceptron extended with independent parameters is applied for that purpose to aluminium alloys AA-7449-T79, AA-2198-T8 and AA-6005A-T6.
This paper deals with the computational modeling and sub-grid scale stabilization of incompressib... more This paper deals with the computational modeling and sub-grid scale stabilization of incompressibility and convection in the numerical simulation of the material flow around the probe tool in a friction stir welding (FSW) process. Within the paradigmatic framework of the multiscale stabilization methods, suitable pressure and convective derivative of the temperature sub-grid scale stabilized coupled thermomechanical formulations have been developed using an Eulerian description. Norton-Hoff and Sheppard-Wright thermo-rigid-viscoplastic constitutive material models have been considered. Constitutive equations for the sub-grid scale models have been proposed and an approximation of the sub-grid scale variables has been given. In particular, algebraic sub-grid scale (ASGS) and orthogonal sub-grid scale (OSGS) methods for mixed velocity, pressure and temperature P1/P1/P1 linear elements have been considered. Furthermore, it has been shown that well known classical C. Agelet de Saracibar (B) · M. Chiumenti · M. Cervera
In this paper a computational model for the numerical simulation of Friction Stir Welding (FSW) p... more In this paper a computational model for the numerical simulation of Friction Stir Welding (FSW) processes is presented. FSW is a new method of welding in solid state in which a shouldered tool with a profile probe is rotated and slowly plunged into the joint line between two pieces of sheet or plate material which are butted together. Once the
Journal of Heat Transfer, 2008
The paper shows the intrinsic difficulties found in the numerical simulation of industrial castin... more The paper shows the intrinsic difficulties found in the numerical simulation of industrial casting processes using finite element (FE) analysis. Up until now, uncoupled pure thermal simulations have been mostly considered to model solidification and cooling phenomena. However, a fully coupled thermomechanical analysis provides a more complete insight of the casting process and the final outcome regarding the quality of the part. In this type of analysis, the thermomechanical model used plays a role of paramount importance, as the problem is coupled both ways through contact between part and mould.
International Journal of Plasticity, 1999
This paper deals with a numerical formulation for coupled thermoplastic problems including phase-... more This paper deals with a numerical formulation for coupled thermoplastic problems including phase-change phenomena. The ®nal goal is to get an accurate, ecient and robust numerical model, allowing the numerical simulation of solidi®cation processes in the metal casting industry. Some of the current issues addressed in the paper are the following. A fractional step method arising from an operator split of the governing dierential equations has been used to solve the nonlinear coupled system of equations, leading to a staggered product formula solution algorithm. Nonlinear stability issues are discussed and isentropic and isothermal operator splits are formulated. Within the isentropic split, a strong operator split design constraint is introduced, by requiring that the elastic and plastic entropy, as well as the phasechange induced elastic entropy due to the latent heat, remain ®xed in the mechanical problem. The formulation of the model has been consistently derived within a thermodynamic framework. The constitutive behavior has been de®ned by a thermoelastoplastic free energy function, including a thermal multiphase change contribution. Plastic response has been modeled by a J2 temperature dependent model, including plastic hardening and thermal softening. A brief summary of the thermomechanical frictional contact model is included. The numerical model has been implemented into the computational Finite Element code COMET developed by the authors. A numerical assessment of the isentropic and isothermal operator splits, regarding the nonlinear stability behavior, has been performed for weakly and strongly coupled thermomechanical problems. Numerical simulations of solidi®cation processes show the performance of the computational model developed. #
International Journal of Plasticity, 2004
This paper exploits the concept of orthogonal sub-grid scales to stabilize the behaviour of mixed... more This paper exploits the concept of orthogonal sub-grid scales to stabilize the behaviour of mixed linear/linear simplicial elements (triangles and tetrahedra) in incompressible or nearly incompressible situations. Both incompressible elastic and J2-plastic constitutive behaviours have been considered. The different assumptions and approximations used to derive the method are exposed. Implementation and computational aspects are also discussed, showing that a robust application of the proposed formulation is feasible. Numerical examples show that the elements derived are free of volumetric locking and spurious oscillations of the pressure, and that the results obtained compare favourably with those obtained with the Q1P0 quadrilateral.
International Journal of Plasticity, 2001
This paper deals with a thermodynamically consistent numerical formulation for coupled thermoplas... more This paper deals with a thermodynamically consistent numerical formulation for coupled thermoplastic problems including phase-change phenomena and frictional contact. The ®nal goal is to get an accurate, ecient and robust numerical model, able for the numerical simulation of industrial solidi®cation processes. Some of the current issues addressed in the paper are the following. A fractional step method arising from an operator split of the governing dierential equations has been used to solve the nonlinear coupled system of equations, leading to a staggered product formula solution algorithm. Nonlinear stability issues are discussed and isentropic and isothermal operator splits are formulated. Within the isentropic split, a strong operator split design constraint is introduced, by requiring that the elastic and plastic entropy, as well as the phase-change induced elastic entropy due to the latent heat, remain ®xed in the mechanical problem. The formulation of the model has been consistently derived within a thermodynamic framework. All the material properties have been considered to be temperature dependent. The constitutive behavior has been de®ned by a thermoviscous/ elastoplastic free energy function, including a thermal multiphase change contribution. Plastic response has been modeled by a J2 temperature dependent model, including plastic hardening and thermal softening. The constitutive model proposed accounts for a continuous transition between the initial liquid state, the intermediate mushy state and the ®nal solid state taking place in a solidi®cation process. In particular, a pure viscous deviatoric model has been used at the initial¯uid-like state. A thermomecanical contact model, including a frictional hardening and temperature dependent coupled potential, is derived within a fully consistent thermodinamical theory. The numerical model has been implemented into the computational International Journal of Plasticity 17 www.elsevier.com/locate/ijplas 0749-6419/01/$ -see front matter # 2001 Elsevier Science Ltd. All rights reserved. P I I : S 0 7 4 9 -6 4 1 9 ( 0 0 ) 0 0 0 9 4 -2 (C. Agelet de Saracibar).
Computer Methods in Applied Mechanics and Engineering, 1999
Computer Methods in Applied Mechanics and Engineering, 2002
In this paper a stabilized finite element method to deal with incompressibility in solid mechanic... more In this paper a stabilized finite element method to deal with incompressibility in solid mechanics is presented. A mixed formulation involving pressure and displacement fields is used and a continuous linear interpolation is considered for both fields. To overcome the Babu s ska-Brezzi condition, a stabilization technique based on the orthogonal sub-scale method is introduced. The main advantage of the method is the possibility of using linear triangular or tetrahedral finite elements, which are easy to generate for real industrial applications. Results are compared with standard Galerkin and Q1P0 mixed formulations for nearly incompressible problems in the context of linear elasticity.
Computer Methods in Applied Mechanics and Engineering, 2003
This paper exploits the concept of orthogonal sub-grid scales to stabilize the behaviour of mixed... more This paper exploits the concept of orthogonal sub-grid scales to stabilize the behaviour of mixed linear/linear simplicial elements (triangles and tetrahedra) in incompressible or nearly incompressible situations. Both incompressible elastic and J2-plastic constitutive behaviours have been considered. The different assumptions and approximations used to derive the method are exposed. Implementation and computational aspects are also discussed, showing that a robust application of the proposed formulation is feasible. Numerical examples show that the elements derived are free of volumetric locking and spurious oscillations of the pressure, and that the results obtained compare favourably with those obtained with the Q1P0 quadrilateral.
Computer Methods in Applied Mechanics and Engineering, 2004
This paper describes a novel formulation for the solution of problems involving shear band locali... more This paper describes a novel formulation for the solution of problems involving shear band localization using a local isotropic J 2 continuum damage model and mixed linear simplex (triangles and tetrahedra). Stabilization methods are used to ensure existence and uniqueness of the solution, attaining global and local stability of the corresponding discrete finite element formulation. Consistent residual viscosity is used to enhance robustness and convergence of the formulation. Implementation and computational aspects are also discussed. A simple isotropic local J 2 damage constitutive model is considered, either with linear or exponential softening. The softening modulus is regularized according to the material mode II fracture energy and the element size. Numerical examples show that the formulation derived is fully stable and remarkably robust, totally free of volumetric locking and spurious oscillations of the pressure. As a consequence, the results obtained do not suffer from spurious mesh-size or mesh-bias dependence, comparing very favourably with those obtained with the ill-posed standard approaches. , strategy, a variant of the first, the nonlinear constitutive laws, for plasticity or damage, are made dependent not only on the local inelastic strain, but also on its second gradient, which is computed according to some additional relation which couples it to the local strain, . In the third, micropolar, strategy, the usual non-polar description of Continuum Mechanics is substituted by other nonstandard theory, like the CosseratÕs continuum, see, for instance, [9] and [10]. In the fourth, viscous-regularized, strategy, the rate-independent format is substituted by a regularized version, also dependent on the strain-rate, see .
Advanced Modeling and Simulation in Engineering Sciences, 2015
Friction Stir Welding (FSW) process is a relatively recent welding process. It was invented at Th... more Friction Stir Welding (FSW) process is a relatively recent welding process. It was invented at The Welding Institute (UK) in 1991. FSW is a solid-state joining process during which materials are not melted. Thus, the heat-affected zone (HAZ) is smaller and the quality of the welding is better with respect to more classical welding processes. In spite of the important number of applications of the FSW, the phenomena happening during the welding are still not well understood. Therefore, the investigations on this process and especially regarding numerical simulations are still very active, see e.g. . A rotating non-consumable tool is inserted between the two work-pieces and displaced along the welding direction (see ). The tool is composed of two parts: a pin and a shoulder. The pin is introduced into the welded joint to mix deeply the two materials together. The aim of the shoulder is to contain the material flow around the pin. As the material in the neighbourhood of the tool is submitted to extremely high strains, resulting from the mechanical intermixing of the two materials by the tool, advanced numerical simulation techniques have to be extended and developed in order to track the correct material deformation. One of these possible extended techniques is the Arbitrary Lagrangian Eulerian (ALE) formulation. This formulation is used to control the mesh displacement regardless of the real material displacement. It is also used to keep a correct mesh quality during the computation . Sometimes, it is also necessary to remesh at least a fraction of the simulation domain. During these remeshing phases, data are transferred thanks to an original method based on a linear reconstruction of the field on an auxiliary finite volume mesh .
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Papers by Michele Chiumenti