Glass Stability Changes the Nature of Yielding under Oscillatory Shear

We perform molecular dynamics simulations to investigate the effect of a glass preparation on its yielding transition under oscillatory shear. We use swap Monte Carlo to investigate a broad range of glass stabilities from poorly annealed to highly stable systems. We observe a qualitative change in the nature of yielding, which evolves from ductile to brittle as glass stability increases. Our results disentangle the relative role of mechanical and thermal annealing on the mechanical properties of amorphous solids, which is relevant for various experimental situations from the rheology of soft materials to fatigue failure in metallic glasses.

Figure 1

(a)–(c) Various rheological quantities as a function of the strain amplitude ${\gamma }_0$ for different $T_{\mathrm{init}}$’s [see the legend shown in (a)]. (a) Stress amplitude ${\sigma }_0$. (b) Phase lag ${\delta }_0$. (c) Storage modulus $G^{\prime }$. Dashed vertical lines in these figures represent the discontinuous jumps of these quantities. (d) The magnitude of the discontinuities of these quantities at yielding as a function of $1/T_{\mathrm{init}}$ vanishes at $T_c\approx 0.1$.

Figure 2

(a) Steady-state inherent structure energy $E_{\mathrm{IS}}$ as a function of the strain amplitude ${\gamma }_0$ for several $T_{\mathrm{init}}$. The dashed vertical lines represent the discontinuous jumps. (b) Nonequilibrium phase diagram in the $({\gamma }_0,T_{\mathrm{init}}^{-1})$ plane. The critical temperature $T_c$ (red long dashed line) divides the phase space into the mechanical annealing (MA) and thermal annealing (TA) regimes. The black solid line separates the elastic and yielded regions (see the text).

Figure 3

The snapshots show a color map of the one-cycle nonaffine deformation $d_{\mathrm{NA},i}$ for (a) $T_{\mathrm{init}}=0.5$ and (b) 0.075 after $n=10$, 30, and 200 cycles (from top to bottom). (c) Evolution of the shear-band order parameter $|H|$. The arrows indicate the times shown in (a),(b). Yielding in (a) is accompanied by the slow emergence of a diffusive shear band, whereas in (b) a sharp shear band is suddenly formed when the material fails macroscopically. Data obtained using the AQS protocol and $N=48000$ with ${\gamma }_0=0.11$.