Thixotropic rheology of semisolid metal suspensions

Understanding the time-dependent flow behavior of semisolid materials (SSM) is essential for the simulation of semisolid processes. During processing, the structure of the material changes with the processing history due to agglomeration and de-agglomeration of particles or particle-particle interactions. Analysis of experimental results show that the transient behavior of SSM at constant structure is shear thickening, and there exists a shear-dependent finite yield stress. The flow of SSM is modeled using the Herschel-Bulkley fluid model. The yield stress, the consistency index, and the power-law index are assumed to be functions of the solid volume fraction and a structural parameter that changes with the processing history. The evolution of the structural parameter is described by a first-order kinetic differential equation. The model is implemented into a 3-d computer code to predict the isothermal how field, yield surfaces, and distribution of parameters in a channel dow. (C) 2001 Published by Elsevier Science B.V.