The yielding behavior 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 G”. At intermediate frequencies a novel, for hard sphere glasses, double peak in G” 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.

From: N. Koumakis, J. F. Brady, and G. Petekidis
“Complex Oscillatory Yielding of Model Hard-Sphere Glasses“, Physical Review Letters 110(17), 178301 (2013).