On the stress overshoot in cluster crystals under shear

Abstract

Using non-equilibrium molecular dynamics simulations we study the yielding behaviour of a model cluster crystal formed by ultrasoft particles under shear. We investigate the evolution of stress as a function of strain for different shear rates, , and temperatures. The stress-strain relation displays a pronounced maximum at the yielding point; the height of this maximum, σp, increases via a power law with an increasing shear range and tends to saturate to a finite value if the limit shear rate goes to zero (at least within the considered temperature range). Interestingly, this behaviour can be captured by the Herschel-Bulkley type model which, for a given temperature, allows us to predict a static yield stress σp0 (in the shear rate tending to zero limit), a characteristic timescale τc, and the exponent α of the above-mentioned power-law decay of the σp at high shear rates. Furthermore, for different temperatures, the σp can be scaled as functions of onto a single master curve when scaled by corresponding τc and σp0. Moreover, for a given shear rate, σp displays a logarithmic dependence on temperature. Again, the σp–T curves for different shear rates can be scaled on a single logarithmic master curve when scaled by a corresponding fitting parameters.