Loading-rate-independent delay of catastrophic avalanches in a bulk metallic glass.

S H Chen,F F Wu,L Xia,G Wang,J L Ren,K C Chan,K A Dahmen,P K Liaw,J Li

doi:10.1038/srep21967

Abstract

The plastic flow of bulk metallic glasses (BMGs) is characterized by intermittent bursts of avalanches, and this trend results in disastrous failures of BMGs. In the present work, a double-side-notched BMG specimen is designed, which exhibits chaotic plastic flows consisting of several catastrophic avalanches under the applied loading. The disastrous shear avalanches have, then, been delayed by forming a stable plastic-flow stage in the specimens with tailored distances between the bottoms of the notches, where the distribution of a complex stress field is acquired. Differing from the conventional compressive testing results, such a delaying process is independent of loading rate. The statistical analysis shows that in the specimens with delayed catastrophic failures, the plastic flow can evolve to a critical dynamics, making the catastrophic failure more predictable than the ones with chaotic plastic flows. The findings are of significance in understanding the plastic-flow mechanisms in BMGs and controlling the avalanches in relating solids.

Highlights

Hassan et al.[28] have reported tremendous increases in fracture toughness of some Zr-based bulk metallic glasses (BMGs) under mixed mode (I/II) conditions
The stress concentration of both notches ensures the fracture occurring through a path, as shown in Fig. 1a, demonstrating several catastrophic avalanches before the fracture
Since in this work we mainly focus on the plastic deformation behavior of the regions between two notches and the facture of BMGs under varying mode mixity has been documented[27–32], the effect of varying mode mixity (I/II) on the fracture of the present specimens is not discussed in detail here

Summary

Introduction

Hassan et al.[28] have reported tremendous increases in fracture toughness of some Zr-based BMGs under mixed mode (I/II) conditions. A recent work of Narayan et al.[30] has shown that BMGs are susceptible to a large variability of mode I fracture toughness while the mode II fracture toughness is relatively more stable. The fracture behavior of BMGs under varying mode mixity (I/II) has been widely studied[27–32], the plastic-flow dynamics as well as the delay of the catastrophic avalanches under a complex stress field has yet to be reported. Differing from the strain-rate-dependent plastic flow in compression tests of BMGs with the presence of uniform stress states[33–35], such a delay of disastrous failure in the present work is found to be independent of loading rate

Methods

Results

Conclusion