8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P8.22Thu 811:10-14:00Nonlinear stress-strain relationship in a glass formingcolloidal mixture under steady shearAmit Kumar Bhattacharjee, 1 Jürgen Horbach, 1 and Thomas Voigtmann 21 Institut für Materialphysik im Weltraum, Deutsches Zentrum für Luft- und Raumfahrt(DLR), Linder Höhe 51147, Köln, Germany2 Zukunftskolleg und Fachbereich Physik, Konstanz, GermanyThe transient and the steady state response of a dense supercooled liquid under steady shear isa poorly understood problem, as the puzzle lies on how the macroscopic response can be derivedfrom a microscopic description. In addition, slow relaxation processes lead to significant history effectsin the case of time-dependent shear. We investigate how these nonlinear response effects arisefrom microscopic processes, and how they depend on the inter-particle interactions. To this end,we have performed a molecular dynamics (MD) simulation of dense colloidal particles of equalsizes interacting through a Weeks-Chandler-Andersen (WCA) potential and compared our resultswith the previous simulations of Yukawa fluid mixture. Below the glass transition temperature, (a)the overshoot in shear stress after the application of a steady shear rate, (b) shear-induced accelerationof the dynamics with a superdiffusive regime intermediate to the ballistic regime at earlystage and diffusive regime at late stage, and (c) shear thinning of the system for higher shear rateare some of the nonlinear responses observed in experiments, found in MD simulations of Yukawamixtures and also understood within a theoretical framework of mode-coupling theory. Our resultsindicate that the amount of stress overshoot is significantly lower in the WCA fluid compared tothe Yukawa fluid, as also found in experiment with hard spheres. We also address to the nonlinearstress-strain response under reversal of the shear rate, both during the initial, reversible, elasticdeformation stage after startup of shear, and from the plastic-flow regime. A significant historydependence of the stress response is observed, which can be related to the “Bauschinger effect”known from the engineering literature, where one observes a lesser yield strength in the reversedshear direction than the forward direction.22