A prediction model of failure threshold for shear deformation in a Zr-based bulk metallic glass

The failure of bulk metallic glasses (BMGs) during plastic deformation at room temperature is abrupt and instantaneous, while the analysis of precursor information based on avalanche events helps predict catastrophic failure. An acoustic emission (AE) signal can provide accurate precursor information for material failure, due to its sensitive and high fast calculation ability. In the current study, AE monitoring tests are carried out during uniaxial compression tests of BMGs at different strain rates. The AE experimental failure threshold, Emax, is proposed on the basis of AE cumulative energy, which reflects the intensity of damage evolution at different loading conditions. Compared with the critical shear band velocity (CSBV) associated with stick-slip dynamics of serrated flow, Emax is a more sensitive failure parameter since it is connected with the local microscopic changes that occur during the material response process. Here, the Emax is obtained prior to reaching the CSBV since the calculation of these two avalanches analysis focuses on the different stages of shear band growth. In particular, AE events are related to the "dry" friction process in the first stage, however, the CSBV is responsible for the "viscous" glide in the second stage. Therefore, Emax is not affected by the complex interactions between the shear bands during the stick-slip process. The maximum avalanche of serrated flow, Smax, is proposed as the experimental failure threshold, which depends on the applied strain rate as Smax similar to epsilon-lambda. According to the relationship of Emax and Smax, the theoretical failure threshold, Emax, follows a criterion Emax = 2545 epsilon-lambda- 4468, where lambda is equivalent to 0.15 for this work. Combining the different calculations and AE measurements, this model gives new insights to predict the deformation failure behavior of Zr-based BMGs.