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See detailSemi-solid constitutive modeling for the numerical simulation of thixoforming processes.
Koeune, Roxane ULg

Doctoral thesis (2011)

Semi-solid thixoforming processes rely on a material microstructure made of globular solid grains more or less connected to each other, thus developing a solid skeleton deforming into a liquid phase ... [more ▼]

Semi-solid thixoforming processes rely on a material microstructure made of globular solid grains more or less connected to each other, thus developing a solid skeleton deforming into a liquid phase. During processing, the material structure changes with the processing history due to the agglomeration of the particles and the breaking of the grains bonds. This particular evolutive microstructure makes semi-solid materials behave as solids at rest and as liquids during shearing, which causes a decrease of the viscosity and of the resistance to deformation while shearing. Thixoforming of aluminum and magnesium alloys is state of the art and a growing number of serial production lines are in operation all over the world. But there are only few applications of semi-solid processing of higher melting point alloys such as steel. This can partly be attributed to the high forming temperature combined with the intense high temperature corrosion that requires new technical solutions. However the semi-solid forming of steels reveals high potential to reduce material as well as energy consumption compared to conventional process technologies, such as casting and forging. Simulation techniques exhibit a great potential to acquire a good understanding of the semi-solid material process. Therefore, this work deals with the development of an appropriate constitutive model for semi-solid thixoforming of steel. The constitutive law should be able to simulate the complex rheology of semi-solid materials, under both steady-state and transient conditions. For example, the peak of viscosity at start of a fast loading should be reproduced. The use of a finite yield stress is appropriate because a vertical billet does not collapse under its own weight unless the liquid fraction is too high. Furthermore, this choice along with a non-rigid solid formalism allows predicting the residual stresses after cooling down to room temperature. Several one-phase material modeling have been proposed and are compared. Thermo-mechanical modeling using a thermo-elasto-viscoplastic constitutive law has been developed. The basic idea is to extend the classical isotropic hardening and viscosity laws to the non solid state by considering two non-dimensional internal parameters. The first internal parameter is the liquid fraction and depends on the temperature only. The second one is a structural parameter that characterizes the degree of structural build up in the microstructure. Those internal parameters can depend on each other. The internal parameters act on the the viscosity law and on the yield surface evolution law. Different formulations of viscosity and hardening laws have been proposed and are compared to each other. In all cases, the semi-solid state is treated as a particular case, and the constitutive modeling remains valid over the whole range of temperature, starting from room temperature to above the liquidus. These models are tested and illustrated by mean of several representative numerical applications. [less ▲]

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See detailNUMERICAL SIMULATIONS OF THIXOFORMING PROCESSES: DEVELOPMENT AND COMPARISON OF SEVERAL SEMI-SOLID CONSTITUTIVE LAWS
Koeune, Roxane ULg; Ponthot, Jean-Philippe ULg

(2011)

ABSTRACT This paper deals with the development, and the comparison, of several constitutive laws in the frame of the simulation of thixoforming processes. The comparison is based on the simulation of a ... [more ▼]

ABSTRACT This paper deals with the development, and the comparison, of several constitutive laws in the frame of the simulation of thixoforming processes. The comparison is based on the simulation of a simple academic test that is well representative of the thixotropic behavior: a simple shear test, with shear-rate step-up and step-down. [less ▲]

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See detailAn improved constitutive model for the numerical simulation of semi-solid thixoforming
Koeune, Roxane ULg; Ponthot, Jean-Philippe ULg

in Journal of Computational & Applied Mathematics (2010), 234

In order to model thixoforming processes, previous papers presented a thermomechanical one-phase modelling. This first version of the constitutive model revealed several limitations: the model could not ... [more ▼]

In order to model thixoforming processes, previous papers presented a thermomechanical one-phase modelling. This first version of the constitutive model revealed several limitations: the model could not degenerate properly to pure solid or liquid behavior nor to free solid suspensions. The aim of this paper was to propose solutions to overcome these limitations. [less ▲]

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See detailValidation of a one-phase thermomechanical model for thixoforming of steel by comparison between numerical and experimental results on two semi-solid extrusion tests
Koeune, Roxane ULg; Rassili, Ahmed ULg; Pierret, Jean-Christophe ULg et al

in Yonglin, Kang (Ed.) 11th International Conference on Semi-Solid Processing of Alloys and Composites (2010)

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See detailSemi-solid metallic alloys modeling for the simulation of thixoforming processes
Koeune, Roxane ULg; Ponthot, Jean-Philippe ULg

in Vaz Jr., M.; de Souza Neto, E. A.; Munoz-Rojas, P. A. (Eds.) Computational Materials Modeling (2010)

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See detailValidation of a one-phase thermomechanical model for thixoforming of steel by comparison numerical and experimental results on two semi-solid extrusion tests.
Koeune, Roxane ULg; Ponthot, Jean-Philippe ULg

(2010)

This paper deals with the simulation of two extrusion tests by thixoforming: a non stationary extrusion test and a double-cup extrusion test. The simulations are based on a thermo-mechanical one-phase ... [more ▼]

This paper deals with the simulation of two extrusion tests by thixoforming: a non stationary extrusion test and a double-cup extrusion test. The simulations are based on a thermo-mechanical one-phase constitutive law that has been presented in details in several previous papers. A campaign of experimental extrusion testing has been conducted on a steel alloy and the comparison between the numerical and experimental results will validate the model under study. A new feature that has been added to the model is also discussed: the introduction of the phase change thermal effects such as the fusion latent heat and the contraction of the material. [less ▲]

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See detailA one-phase thermomechanical constitutive model for the numerical simulation of semi-solid thixoforming
Koeune, Roxane ULg; Ponthot, Jean-Philippe ULg

in International Journal of Material Forming (2008), suppl. 1

A thermomechanical one-phase elasto-visco-plastic constitutive law has been developed in order to model thixoforming processes. The simulation of a simple academic 2D test has revealed the forces and ... [more ▼]

A thermomechanical one-phase elasto-visco-plastic constitutive law has been developed in order to model thixoforming processes. The simulation of a simple academic 2D test has revealed the forces and weaknesses of the proposed model. [less ▲]

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See detailAn Improved Constitutive Model for the Numerical Simulation of Semi-Solid Thixoforming
Koeune, Roxane ULg; Ponthot, Jean-Philippe ULg

in Proceedings of ACOMEN’2008, Advanced Computational Methods in Engineering (2008)

In order to model thixoforming processes, previous papers presented a thermo-mechanical one-phase modelling. This first version of constitutive model revealed several limitations: the model could not ... [more ▼]

In order to model thixoforming processes, previous papers presented a thermo-mechanical one-phase modelling. This first version of constitutive model revealed several limitations: the model could not degenerate properly to pure solid or liquid behaviour neither to free solid suspensions. The aim of this paper was to propose solutions to overcome these limitations. [less ▲]

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See detailA One Phase Thermomechanical Model for Semi-Solid Thixoforming
Koeune, Roxane ULg; Ponthot, Jean-Philippe ULg

in S2P, the 10th International Conference on Semi-Solid Processing of Alloys and Composites (2008)

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See detailA one-phase thermomechanical Model for Semi-Solid thixoforming
Koeune, Roxane ULg; Ponthot, Jean-Philippe ULg

in Solid State Phenomena (2008), 141-143

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See detailA One-Phase Thermomechanical Constitutive Model for the Numerical Simulation of Semi-Solid Thixoforming
Koeune, Roxane ULg; Ponthot, Jean-Philippe ULg

in Proceedings of ESAFORM 2008, Conference on material forming (2008)

A thermo mechanical one-phase elasto-visco-plastic constitutive law has been developed in order to model thixoforming processes. The simulation of a simple academic 2D test has revealed the forces and ... [more ▼]

A thermo mechanical one-phase elasto-visco-plastic constitutive law has been developed in order to model thixoforming processes. The simulation of a simple academic 2D test has revealed the forces and weaknesses of the proposed model. [less ▲]

Detailed reference viewed: 10 (3 ULg)
See detailThermomechanical one-phase modeling of semi-solid thixoforming
Koeune, Roxane ULg; Ponthot, Jean-Philippe ULg

in Int. Conf. on Computational Methods for Coupled Problems in Science and Engineering, COUPLED PROBLEMS 2007 (2007)

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See detailNumerical simulation of semi-solid thixoforming
Koeune, Roxane ULg; Ponthot, Jean-Philippe ULg

in Int. Conf. on Computational Plasticity, COMPLAS IX (2007)

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See detailNumerical simulation of large strain rate dependent J2 problems
GARCIA GARINO, A.; Ponthot, Jean-Philippe ULg; MIRASSO, A. et al

in Proceedings of ENIEF 2006, Mecanica Computational (2006, November)

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See detailDetermination of solidification parameters used for the prediction of the thixoformability of several steel alloys
Lecomte-Beckers, Jacqueline ULg; Rassili, Ahmed ULg; Robelet, Marc et al

in Solid State Phenomena (2006), 116-117

This paper focuses on the liquid fraction curves of several steels and the correlation between liquid fraction, temperature and heating rate. The work has been performed along two main axes. First, the ... [more ▼]

This paper focuses on the liquid fraction curves of several steels and the correlation between liquid fraction, temperature and heating rate. The work has been performed along two main axes. First, the solid fraction versus temperature has been obtained experimentally by differential scanning calorimetry (DSC), limited to low heating rates. Then, a shift of the liquid fraction curves has been noticed at high industrial heating rates. The quantification of this effect could not be carried out by DSC and required the elaboration of another experimental device. [less ▲]

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See detailStudy of the liquid fraction and thermophysical properties of semi-solid steels and application to the simulation of inductive heating for thixoforming
Lecomte-Beckers, Jacqueline ULg; Rassili, Ahmed ULg; Carton, Marc ULg et al

in Bananic, Dorel (Ed.) Advanced Methods in Material Forming (2005)

The thixoforming of steels is so complex that it requires more investigations regarding both the materials and the technical tools dedicated to the elaboration of the process. In this paper we will show ... [more ▼]

The thixoforming of steels is so complex that it requires more investigations regarding both the materials and the technical tools dedicated to the elaboration of the process. In this paper we will show the experimental determination of appropriate solidus-liquidus interval on eight different steel compositions. This critical parameter was obtained using Differential Scanning Calorimetry. The paper also presents the results of thermophysical property determination. These parameters are important for the inductive heating phase of a semi-solid forming (SSF) process. Thanks to the simulations of the inductive heating process, the other main results consist on the developments of the heating techniques that are suitable for the achieving of the sine qua none condition to the semi-solid process, which is the uniform temperature distribution in the reheated billet. [less ▲]

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