On the stress overshoot in cluster crystals under shear

GP Shrivastav and G Kahl, CONDENSED MATTER PHYSICS, 23, 23801 (2020).

DOI: 10.5488/CMP.23.23801

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, (gamma) over dot, and temperatures. The stress-strain relation displays a pronounced maximum at the yielding point; the height of this maximum, sigma(p), 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 sigma(0)(p) (in the shear rate tending to zero limit), a characteristic timescale tau(c), and the exponent alpha of the above-mentioned power-law decay of the sigma(p) at high shear rates. Furthermore, for different temperatures, the sigma(p) can be scaled as functions of (gamma) over dot onto a single master curve when scaled by corresponding tau(c) and sigma(0)(p). Moreover, for a given shear rate, sigma(p) displays a logarithmic dependence on temperature. Again, the sigma(p)-T curves for different shear rates can be scaled on a single logarithmic master curve when scaled by a corresponding fitting parameters.

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