Transient and non-isothermal semi-solid behaviour: 3D micromechanical modelling

Simulating semi-solid metal forming requires modelling of semi-solid behaviour. However, such modelling is difficult because semi-solid behaviour is thixotropic and depends on the liquid-solid spatial distribution within the material. In order to better understand and model the relationships between the microstructure and the behaviour, this paper presents a model based on micromechanical approaches and homogenisation techniques. Shear rate jump tests for solid fraction lower than 0.5 and compression tests for solid fraction higher than 0.5 were simulated. Predicted transient responses for both types of tests are in qualitative agreement with experimental results. The gradual stress decrease in step-change up in shear rate is associated with the disagglomeration of isolated solid aggregates while the sharp fall in load observed in the load-displacement curves originates from a 3D continuous solid skeleton, which suddenly breaks down under load. These microstructural changes are related to the shear rate field distribution.