1. Combined thermal, solutal and momentum transport. Assume a rigid mold. Imperfect contact and air gap formation at metal/mold interface Design of mold surface topography during early stage solidification of Al alloys PI: Prof. Nicholas Zabaras Participating students: Deep Samanta, Lijian Tan Material Process Design and Control Laboratory D. Samanta and N. Zabaras, “A coupled thermomechanical, thermal transport and segregation analysis of the solidification of Aluminum alloys on molds of uneven topographies ”, Materials Science and Engineering: A, in press. Lijian Tan, Nicholas Zabaras, “A thermomechanical study of the effects of mold topography on the solidification of Aluminum alloys", Materials Science and Engineering: A, Vol. 404, 197-207, 2005. D. Samanta and N. Zabaras, “Numerical study of macrosegregation in Aluminum alloys solidifying on uneven surfaces”, International Journal of Heat and Mass Transfer, Vol. 48, 4541-4556, 2005. L. Tan, D. Samanta and N. Zabaras, “A coupled thermomechanical, thermal transport and segregation analysis of the solidification of aluminum alloys on molds of uneven surface topographies”, Proceedings of the 3rd M.I.T. Conference on Computational Fluid and Solid Mechanics, Massachusetts Institute of Technology, Cambridge, MA, June, 2005. Selected publications Parametric analysis for the following parameters: 1) Wavelength(λ) 2) Concentration (C Cu ) 3) Superheat (ΔT melt ) Low solid fractions usually accompanied by melt feeding. With increase in solid fraction, there is an increase in strength and bonding ability of dendrites. Left: Evolution of pressure at trough with time at selected wavelengths. Right: Mean shell thickness at gap nucleation time. Cornell University College of Engineering Sibley school of Mechanical and Aerospace Engineering Surface defects in casting Sub-surface liquation Crack formation Ripple formation Uneven mold surface topography effects Undesirable growth using plain mold Desirable growth using uneven mold Modeling effects of uneven mold surface on solidification Fluid flow Heat transfer Casting domain Heat transfer Mold Contact pressure/ air gap criterion Solute transport Inelastic deformation Phase change and mushy zone evolution Deformable or non-deformable mold Heat transfer in the mold, solid shell and melt. Heat transfer causes deformation (thermal stress). Gaps or contact pressure affect heat transfer. Solidification after air-gap nucleation not modeled. Gap nucleation time (comparison with analytical study) Al-Cu alloy with 1.8% Cu is most susceptible to hot tearing Wavelength less than 5mm corresponds to an optimum Surface tension effects Initial contact between mold and liquid The size of micro-gap Heat flux at early stages of solidification Surface quality of aluminum casting Mold topographySurface energyGravity A change of surface tension drastically changes the solidification speed at very early stages of solidification. Micro-scale effects Macro-scale effects Equivalent stress (t = 0.1 s) Isotherms (t = 0.1s) λ = 3 mm λ = 5 mm