10:00 AM - 10:15 AM
[SCG59-10] Shear-induced instability of an aging suspension
For this reason, instead of using real magma but by using analog material this study aims to reveal possible control of complex rheology in magma flow dynamics. We particularly focus on shear-induced instability of the suspension such as shear-banding phenomena to drive unstable and oscillatory flows. As an analog material we utilized an aging suspension of fine silica particles (Ludox TM-40, Aldrich) with salt water. The suspension is known to have yield stress, aging behavior and thixotropic natures [Moller et al., 2008], which can be an analog for the magma complexity. A series of rheological experiments with the use of a rheometer (AR1000, TA Instrument) and 1D and 2D ultrasonic speckle velocimetries (USV) [S. Manneville, 2004] have achieved to observe global rheology and local velocity profiles in the flow simultaneously. By results from the experiments under various conditions changing applied shear rate and aging time, we conclude that the flow behavior can be divided into three types; fluidization, unstable shear banding, and stable shear banding. In the cases of fluidization and unstable shear banding, shear stress fluctuates when the width of shear band and slip velocity show large shift. In this way, it was revealed that fluctuation of shear stress could occur in this kind of suspension and both shear-banding and wall-slip are responsible for driving the shear-induced global instability.