A well defined glass state obtained by oscillatory shear

We investigate the process of shear melting and resolidification of a colloidal glass, directly after loading (preyielding) and after a series of consecutive strain sweeps (postyielding). The postyielding glass shows a significant softening compared with the preyielding glass, together with the absence of history effects in successive shear melting protocols, indicating a reproducible process of fluidisation and resolidification into a glass state unaffected by residual stresses. However, a significant hysteresis characterizes strain sweeps with increasing or decreasing strain amplitude. The appearance of history and hysteresis effects coincides with the formation of a glass state, whereas it is not observed in the liquid. We can describe the onset of shear melting over a broad range of volume fractions and frequencies using a recently developed model which describes the yielding process in terms of loss of long-lived nearest neighbors.