Cavitation-Induced Fracture Causes Nanocorrugations in Brittle Metallic Glasses

Brittle metallic glasses exhibit a unique and intriguing fracture morphology of periodic nanocorrugations whose spacing and amplitude are of the order of tens of nanometers. We show through continuum simulations that they fail by spontaneous and simultaneous cavitation within multiple weak zones arising due to intrinsic atomic density fluctuations ahead of a notch tip. Dynamic crack growth would then occur along curved but narrowly confined shear bands that link the growing cavities. This mechanism involves little dissipation and also explains the formation of nanocorrugations.

Figure 1

(a) Schematic showing three weak zones indicated as WZ-I, WZ-II, and WZ-III ahead of a notch tip. Variation of the normalized macroscopic hydrostatic stress ${\mathrm{\Sigma }}_{hw}/{\sigma }_o$ and relative increase in the corresponding void areas $(A-A_o)/A_o$ with $K/({\sigma }_o\sqrt{L_o})$ corresponding to the weak zone (b) WZ-I, (c) WZ-II, and (d) WZ-III for ${\sigma }_{ow}/{\sigma }_o=0.1$. The stage at which cavitation occurs in the respective weak zones is marked by “cross” symbols.

Figure 2

Contour plots of the maximum principal logarithmic plastic strain $\log {\lambda }_1^p$ at $K/({\sigma }_o\sqrt{L_o})$ of (a) 0.67, (b) 0.96, (c) 1.21, (d) 1.45, (e) 2.09, and (f) 2.37 for ${\sigma }_{ow}/{\sigma }_o=0.1$. Potential crack paths along which crack propagation is likely to occur are indicated by black dashed lines. A simulation movie is available in the Supplemental Material [36].

Figure 3

(a) Contours of plastic strain obtained from a simulation of the full domain showing a curved SB linking the notch tip with void I. (b) Schematic depicting the potential crack path deduced on the basis of (a).

Figure 4

Contour plots of the maximum principal logarithmic plastic strain $\log {\lambda }_1^p$ at $K/({\sigma }_o\sqrt{L_o})$ of (a) 1.58, (b) 1.72, (c) 2.34, and (d) 2.52 for ${\sigma }_{ow}/{\sigma }_o=0.6$. The potential crack paths along which crack propagation is likely to occur are indicated by black dashed lines. (e) Variation of the plastic work $U^p$ per unit thickness normalized by $U_o={\sigma }_o{L}_o^2$ with $K/({\sigma }_o\sqrt{L_o})$ for different values of ${\sigma }_{ow}/{\sigma }_o$. The stage at which cavitation occurs in WZ-I is indicated by the “cross” symbol and that pertaining to fracture initiation (when the notch tip links with void I following failure in a curved SB) is indicated by the “circle” symbol.