2, Joint International Research Laboratory of Impact Dynamics and Engineering Application, Xi'an, , China
3, Shaanxi Key Laboratory of Impact Dynamics and Engineering Application, Xi'an, , China
Bulk Metallic Glasses (BMGs) have shown increasing promise as engineering materials because of their excellent mechanical, physical and biomedical properties. Different from crystal materials, the plastic deformation of BMGs is localized in narrow shear bands, in which local strain is accommodated by 'shear transformation'. Such an event essentially refers to atomic clusters undergo a shear displacement. While originated from inelastic shear distortion, shear banding behavior in BMGs is strongly affected by normal stress. Thus, it is of great importance to study the intrinsic properties of BMGs under shear-dominated loading condition. This study focuses on shear banding and fracture behavior in BMGs under quasi-static and dynamic shearing. With specially designed double-shear sample, shear-dominated stress state is achieved in the shear zones of the sample. The shear responses of BMGs under quasi-static and dynamic loading rates are measured by test machine and modified split Hopkinson pressure bar. Meanwhile, in-situ high-speed photographing is used to capture the real-time deformation process from shear-band initiation and propagation to fracture. Digital image correlation (DIC) is introduced to measure the real-time strain evolution. Combined with shear responses, real-time deformation images and SEM observations, we conclude the strain-rate effect on the mechanical properties of BMGs under shear loading. The plastic deformation is dominated by multiple shear banding under quasi-static shearing, while dominated by single shear banding under dynamic shearing. In addition, rate effect on the transition from shear band to crack is studied owing to the absence of normal stress effect during shear banding process. The transition is originated from cavity formation along a shear band under quasi-static loading, while from direct crack-opening at shear band tip under dynamic loading. The rate effect on shear-band-to-crack transition might be due to growing temperature rise within shear bands with increasing strain rate.