Dynamic Failure Mechanisms in Beryllium-Bearing Bulk Metallic Glasses

摘要

The understanding of dynamic failure mechanisms in bulk metallic glasses is important for the applciation of this class of matrials ot a variety of engineering problems. This is true not only for design environments in which components are subject to high loading rates, but also when components are subjected to quasi-static loading conditions where observations have been made of damage propagation occurring in an unstable, highly dynamic manner. This paper presents preliminary results of a study of the phenomena of dynmaic crack initiation and growth as well as the phenomenon of dynamic lcalization in a beryllium-bearing bulk metallic glass, Zr sub 41.25Ti sub 13.75Ni sub 10Be sub 22.5. pre-notched and pre-fatigued plate spectimens were subjected to quasi-static and dynamic three-point bend loading to investigate crack initiation and propatation. Asymmetric ipact loading with a gas gun was used ot induce dynamic shear band growth. The mechanical fields in the vicinity of the dynamically loaded crack or notch tip were characterized using high-speed optical diagnostic techniques. The results demonstrated a dramatic increase in the crack initiation toughness with loading rate and subsequent crack tip speeds approaching 1000 m s sup -1. Dynamic crack tip branchign was also observed under certain conditions. Shear bands formed readily under asymmetric impact loading. The shear bands traveled at speeds fo approximately 1300 m s sup -1 and were accompanied by intense loaclized heating measured using high-speed full-field infrared imaging. The maximum temperatures recorded across the shear bands were in excess of 1500K.