Computer simulation of the microstructure and rheology of semi-solid alloys under shear

The rheological behavior of metallic alloys containing both solid and liquid phases is investigated in the low solid fraction range (<50%). This behavior depends on both the solid fraction and the shear rate. The concept of Effective Volume Fraction (EVF) is used to decorrelate the influence of these two parameters. At high shear rate the slurry behaves like a suspension of hard spheres, whereas at lower shear rate, particles tend to aggregate in clusters, entrapping liquid and thus, increasing the EVF and the viscosity. A lattice model is introduced to simulate the aggregation / break-up processes within a slurry under shear. When the steady state is reached, the entrapped liquid fraction is calculated, leading to a viscosity estimation. Simulation results for the viscosity and 3D cluster structure are in good agreement with experimental results.Comment: 30 pages, 17 figures, to be published in Acta Mate

Nonequilibrium phase transition in the kinetic Ising model: Is transition point the maximum lossy point ?

The nonequilibrium dynamic phase transition, in the kinetic Ising model in presence of an oscillating magnetic field, has been studied both by Monte Carlo simulation (in two dimension) and by solving the meanfield dynamical equation of motion for the average magnetization. The temperature variations of hysteretic loss (loop area) and the dynamic correlation have been studied near the transition point. The transition point has been identified as the minimum-correlation point. The hysteretic loss becomes maximum above the transition point. An analytical formulation has been developed to analyse the simulation results. A general relationship among hysteresis loop area, dynamic order parameter and dynamic correlation has also been developed.Comment: 8 pages Revtex and 4 Postscript figures; To appear in Phys. Rev.