108 research outputs found
Complex oscillatory yielding of model hard sphere glasses
The yielding behaviour of hard sphere glasses under large amplitude
oscillatory shear has been studied by probing the interplay of Brownian motion
and shear-induced diffusion at varying oscillation frequencies. Stress,
structure and dynamics are followed by experimental rheology and Browian
Dynamics simulations. Brownian motion assisted cage escape dominates at low
frequencies while escape through shear-induced collisions at high ones, both
related with a yielding peak in\ . At intermediate
frequencies a novel, for HS glasses, double peak in is
revealed reflecting both mechanisms. At high frequencies and strain amplitudes
a persistent structural anisotropy causes a stress drop within the cycle after
strain reversal, while higher stress harmonics are minimized at certain strain
amplitudes indicating an apparent harmonic response.Comment: 4 figures placed at the end with following order: Figure 1, figure 3,
figure 4 and figure
Yielding of Hard-Sphere Glasses during Start-Up Shear
Concentrated hard-sphere suspensions and glasses are investigated with rheometry, confocal microscopy, and Brownian dynamics simulations during start-up shear, providing a link between microstructure, dynamics, and rheology. The microstructural anisotropy is manifested in the extension axis where the maximum of the pair-distribution function exhibits a minimum at the stress overshoot. The interplay between Brownian relaxation and shear advection as well as the available free volume determine the structural anisotropy and the magnitude of the stress overshoot. Shear-induced cage deformation induces local constriction, reducing in-cage diffusion. Finally, a superdiffusive response at the steady state, with a minimum of the time-dependent effective diffusivity, reflects a continuous cage breakup and reformation
Stress versus strain controlled shear: Yielding and relaxation of concentrated colloidal suspensions
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