(513a) Experimental Decomposition of the Rheological Responses of Elastoviscoplastic Materials

In an effort to gain a deeper understanding of the rheology behind the yielding transition, we perform experimental decompositions of the response of a model yield stress fluid, a Carbopol microgel, to transient shear strains. These decompositions are achieved at different amplitudes of applied shear by means of oscillatory stress jumps (in the case of stress) and oscillatory shear and recovery tests (in the case of strain). The flow cessation and recovery steps are performed at multiple points over the course of a period of oscillation, to accurately map out the decomposition in a thorough manner.

The stress jump tests separate stress acquired through elastic and inelastic processes and show that nearly all the stress in the Carbopol system is elastic. The shear/recovery tests, by contrast, allow for recoverable and unrecoverable strains to be resolved, and show that when above the yield point, both of these components contribute significantly to the overall materials response. We utilize the interplay between these two strain components to develop a more comprehensive rheological picture of yielding in soft materials. These results suggest that any numerical decompositions for yield stress materials need to consider the existence of both unrecoverable viscoplastic flow above the yield point and a recoverable strain which persists once yielding has taken place.