The effect of superposed oscillations on steady state shear thickening

The subject of shear thickening has enjoyed considerable attention of researcher in the 80’s and 90’s, after the classical publications of Hoffman in the 70’s. Barnes reviewed experimental results. Boersma et.al investigated shear thickening both in steady and oscillatory flow and studied its time dependency. They also compared it with computer simulations results based on Stokesian dynamics. Chow and Zukoski carefully studied diffraction patterns of shear thickening suspensions. Kaldasch et al. interpreted shear thickening on the basis of the Landau-Ginzburg theory for phase transactions and as an acoustic resonance phenomenon. More recently, Laven et al. compared elongational thickening and shear thickening and showed that these are essentially different.In order to facilitate the flow of suspensions in technological applications, vibrations are sometimes used in order to facilitate flow or leveling, e.g. in concrete and in ceramics processing. The present authors have the experience that in a rheometer a structure that has been brought in a ‘blocked" state can be relaxed towards a more liquid state by the application of oscillatory shear flow of progressively low amplitude. This was the motivation to study the effect of vibrations superposed on a steady shear flow in a more systematic way. In this study we focused on shear oscillations, either parallel or orthogonal to the steady shear direction.