Reversing strains revisited

Abstract

• Non-colloidal suspensions were tested in large amplitude sinusoidal strains • A reversing flow disengages contact friction in a strain of only about 10 −4 • This sudden disengagement explains the very small linear range of response . We consider strain reversing flow patterns for inelastic non- colloidal suspensions. A main result of this study is that the unlocking of the suspension structure takes place in a very small shear strain (O (10 −4 )) after a strain-rate reversal. This implies that for any computer simulation the motion would have to be continually scanned everywhere to find areas of strain reversal where sudden changes in stress take place We suggest that in oscillatory flow the difficult task of finding the range of linear G’ and G” behaviour of suspensions is also due to the sudden drops in stress upon strain-rate reversal; we expect the linear region of strain to be of the order of magnitude of half the sphere roughness ratio (0.5 of average roughness / sphere radius), which is here about 0.00075.So finding meaningful linear G’ and G” values is always going to be difficult.