Simulation of Semi-Solid Material Mechanical Behavior Using a Combined Discrete/Finite Element Method

Abstract

As a necessary step toward the quantitative prediction of hot tearing defects, a three-dimensional stress-strain simulation based on a combined finite element (FE)/discrete element method (DEM) has been developed that is capable of predicting the mechanical behavior of semisolid metallic alloys during solidification. The solidification model used for generating the initial solid-liquid structure is based on a Voronoi tessellation of randomly distributed nucleation centers and a solute diffusion model for each element of this tessellation. At a given fraction of solid, the deformation is then simulated with the solid grains being modeled using an elastoviscoplastic constitutive law, whereas the remaining liquid layers at grain boundaries are approximated by flexible connectors, each consisting of a spring element and a damper element acting in parallel. The model predictions have been validated against Al-Cu alloy experimental data from the literature. The results show that a combined FE/DEM approach is able to express the overall mechanical behavior of semisolid alloys at the macroscale based on the morphology of the grain structure. For the first time, the localization of strain in the intergranular regions is taken into account. Thus, this approach constitutes an indispensible step towards the development of a comprehensive model of hot tearing.

Three-dimensional granular model of semi-solid metallic alloys undergoing solidification: Fluid flow and localization of feeding

“…Thus important physical phenomena, such as feeding variations at the level of the grains, cannot be obtained to improve hot tearing predictions. Over the past few years a new technique based on granular modeling has shown much promise for investigating the initiation and propagation of cracks within liquid films [14][15][16][17][18][19][20][21][22][23]. In this technique the liquid and solid phases are modeled independently but with a large enough domain size to be considered a RVE.…”

“…Thirdly, the model is validated and then used to explore fluid flow during the globular solidification of an aluminum-copper alloy. The liquid film geometry for the semi-solid fluid flow simulations is created using the 3-D granular solidification model known as GMS-3D [16,23]. In this model it is assumed that the grains are distributed randomly within an RVE of nearly uniform temperature.…”

“…The base of the pyramid is subdivided into triangles so as to only have tetrahedral elements that can be used either in solid deformation [23] or fluid flow calculations (see Fig. 2b).…”

“…1a the grains belonging to the same cluster are shaded the same gray level. Further details of this model, together with a discussion of its limitations and domain of validity, are given in Phillion et al [16] and Sistaninia et al [23].…”

Prediction of Hot Tear Formation in Vertical DC Casting of Aluminum Billets Using a Granular Approach

“…The hydromechanical coupled model for solidification and semisolid deformation, [3][4][5] which was recently developed by Sistaninia et al uses a granular approach to fulfill the above requirements and simulate hot tearing. The use of a granular approach enables each grain to exist as a discrete element while allowing for efficient simulation of an ensemble of grains making up the microstructure.…”