Transient response of concentrated suspensions after shear reversal

We have examined the transient stress response under shear flow of concentrated suspensions of non-Brownian spheres. We focused on the experiment where the shearing is momentarily stopped and restarted in the opposite direction. We found that the normalized stress recovery curves for different values of the initial and subsequent shear rates could be collapsed quite well if plotted against the strain. This behavior agrees with the basic concept that the transient stress behavior is a function only of the imposed strain, as predicted by some recent constitutive models of concentrated suspensions. We also found that the transient behavior of the normal stress difference showed similar data collapse. Further, there appeared to be little qualitative difference in the behavior of particulate systems with a high degree of size monodispersity and those more polydisperse. (C) 2002 The Society of Rheology.