Shear-band-to-crack transition in bulk metallic glasses under quasi-static and dynamic shearing

The intrinsic fracture mechanism of bulk metallic glasses (BMGs) is often obscured with the involvement of normal stress. To decouple the normal-stress effect, a double-notched shearing technique is developed to investigate the mechanical properties of BMGs. Real-time shear banding and fracture behavior under quasi-static and dynamic shearing are captured by using high-speed photographing, which confirms multiple shear banding at low strain rates and single shear banding at high strain rates. More importantly, the transition from shear band to crack could be observed with little influence of normal stress. Such transition is found to be induced by cavitation mechanism and shows obvious rate dependence; that is originated from regularly distributed controllable cavities under quasi-static loading, while from a series of concentrated cavitation under dynamic loading. Referring to studies under compression and tension, we clarify that strain rate controls cavitation concentration level and normal stress controls cavitation instabilities, respectively.