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

On the yielding of a point-defect-rich model crystal under shear: insights from molecular dynamics simulations

“…Of course, within a short time this vacancy will be filled up by another particle arriving from another, neighboring lattice site. In our previous work 55 we have demonstrated that cluster crystals exhibit an overshoot in their stress-strain response. For a fixed temperature, the height of this overshoot decreases with a decreasing shear rate.…”

“…Starting our reasoning from Equ. (9) this master curve has thus the form [33,44]: In panel (b) of Fig. 3 we show this master curve onto which the different σ p ( γ)-curves can be mapped.…”

Elasticity in crystals with high density of local defects : insights from ultra-soft colloids

“…The simulation methodology is similar as in previous contributions 18,[21][22][23] . The GEM-4 potential, defined in Eq.…”