Roxane Koeune

Study of the Liquid Fraction and Thermophysical Properties of Semi-Solid Steels and Application to the Simulation of Inductive Heating for Thixoforming

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.

An improved constitutive model for the numerical simulation of semi-solid thixoforming

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.

Determination of Solidification Parameters Used for the Prediction of the Thixoformability of Several Steel Alloys

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.

A One Phase Thermomechanical Model for Semi-Solid Thixoforming

In order to model thixoforming processes, previous papers presented a thermomechanical 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.

Numerical Simulation of Double Cup Extrusion Test Using the Arbitrary Lagrangian Eulerian Formalism

In this chapter Double Cup Extrusion Test (DCET) is modelled using the finite element method with the help of the Arbitrary Lagrangian Eulerian (ALE) formalism. DCET is a tribological test involving very large deformations which are traditionally dealt with complicated and costly remeshing algorithms. Since the topology of ALE meshes should remain constant throughout the simulation, two very thin layers of auxiliary elements are added to the initial mesh of the billet where the material is expected to flow. This numerical trick is combined with an original and efficient node relocation procedure which allows the model to take into account complex geometries of punches. The presented model is firstly validated for limited punch strokes thanks to a purely Lagrangian simulation. It is then compared with results from the literature. Eventually the general nature and the effectiveness of this numerical strategy is demonstrated by a fully-coupled thermomechanical simulation of thixoforming where the final shape of the billet is compared to experimental measurements.

A Thermomechanical Model Dedicated to Thixoforming. Application to Semi-Solid Forming

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 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.