Strain-hardening and failure mechanisms of metallic glasses under triaxial stress

RT Wan and ZL Long and YX Cui, INTERMETALLICS, 167, 108210 (2024).

DOI: 10.1016/j.intermet.2024.108210

Unlike strain-hardening (the increase of flow stress with plastic strain) due to glide of dislocations in conventional crystalline metals, metallic glasses (MGs) usually exhibit strain-softening, which leads to extreme localization of plastic flow in shear bands. In the present study, triaxial stress states are introduced by fabricating annular notches, and molecular dynamics (MD) simulations have been performed on nanoscale notched MGs to systematically investigate the influence of stress triaxiality on their tensile fracture strengths and failure mechanisms. It is found that the triaxial stress states suppress the formation and rapid extensions of shearbanding and lead to strain- hardening of MGs. With the increase of stress triaxiality, the failure mechanisms of MGs transits from shear-banding to cavitation. In the vicinity of the critical stress triaxiality, the failure mechanism of necking occurs and the strain-hardening effect is the strongest. The reasons are the large degree of free volume growth and recovery at the notch and the large degree of recovery of Cu-centered full-icosahedral fraction. Our study systematically investigates the strain-hardening effect and the transition of the failure mechanisms of MGs below the critical stress triaxiality, at the critical stress triaxiality, and above the critical stress triaxiality, which provides significant insights into the effect of the triaxial stress state on the strainhardening and failure mechanisms of nano-sized MGs.

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