The Study On Effect Of Stress State To Shear Banding Behaviors In Bulk Metallic Glasses

This thesis is aiming to study the effect of stress state to shear banding behaviors in bulk metallic glasses (BMGs), which have a very wide range of applicability as structural materials. For this sake, a series of experiments were performed. The mechanism of stress state to shear banding behaviors in BMGs is illuminated primarily. The results are beneficial to understand the plastic behaviors and give some valuable clues to applications of BMGs.A uniaxial compressive experiment on cylindrical samples with different aspect ratios was used to investigate the effect of lateral stress to shear banding behaviors of a zirconium-based BMG. The results demonstrate that lateral stress mainly affects the quantity of shear bands, and its whether appear bifurcation, intersection and slip or not. In addition, with the increase of influence of lateral stress the produce order of shear banding behaviors can be summarized as: intersection-bifurcation-slip. A controllable shear technique was used to study the effects of normal stress to shear banding behaviors of a zirconium-based BMG. The results demonstrated that normal stress has significant iMPact on the number, inclined angle and length of the shear bands. In addition, the normal stress is the major factor of inducing bifurcation of the main shear bands, the formation of secondary shear bands and their intersection with each other. The intersection and slip of shear bands can increase the plasticity of BMGs.An experiment, which consisted of uniaxial compression of specimens that were encased in special sleeves with different ratios of outer diameter/inner diameter, was used to study the effect of hydrostatic pressure to shear banding behaviors of a zirconium-based BMG. Results showed that the formation of main shear band and secondary shear band were a competitive process. Hydrostatic pressure would promote free volume softening in the interior of BMGs and made shear bands form easily.A possible method, which could introduce the influence of normal stress into the free volume model, is developed to characterize the effect of normal stress on plasticity in BMGs. The calculated results of modified free volume model comply with the results of controlled shear experiments.The experiment results showed that the effects of stress state to shear banding behaviors were obvious. Lateral stress would make the shear banding behaviors change from unidirection shear bands to multiple shear bands, intersection, bifurcation and slip. Normal stress would induce the bifurcation of the main shear bands, the formation of secondary shear bands and intersections with each other. Hydrostatic pressure would promote free volume softening in the interior of BMGs and the formation of shear bands.