Numerical study of the notch effect on the malleability of bulk metallic glasses based on the free-volume theory
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In this paper, numerical study was systematically conducted to analyze the shear banding evolution in bulk metallic glasses (BMGs) with various notches subjected to the uniaxial compression, and the relation between the notched configurations and compressive malleability was therefore elucidated. Free volume was used to be an internal state variable to depict the shear banding nucleation, growth and coalescence in the BMGs with the aid of free volume theory, which was incorporated into ABAQUS finite element method code as a user material subroutine. The present numerical procedure was firstly verified by comparing with the existing experimental data, and then parameter analysis was performed to discuss the impacts of notch shape, notch size, notch orientation, and notch configuration on the plastic deformability of notched samples. The present modeling will shed some light on the failure mechanisms and the toughening design of notched BMG structures in the engineering applications.
I. INTRODUCTION
Bulk metallic glasses (BMGs) have many unique properties, e.g., exceptionally high strength, large elastic limit, high hardness, good corrosion resistance, and reduced sliding friction, etc., and are therefore regarded as potential candidates of engineering materials. However, their structural applications are severely stymied by their intrinsic limited plasticity that is confined to narrow regions near dilute shear bands at room temperature. To make BMGs tough, many techniques have been gradually developed. It is commonly accepted that multiaxial stress field is identified to efficiently initiate the proliferation of shear bands and effectively impede their rapid propagation. Among these measures, introducing notches could markedly enhance the plasticity of BMGs, and the toughening efficiency could largely rely on many factors, and the inherent mechanism in the notched BMGs is still poorly understood. On the other hand, understanding notch-related failure is also crucial for the design of reliable engineering structures, but the underlying physical mechanism responsible for the amorphous materials is far from being revealed. Up to date, many relevant researches have been performed to analyze the effect of notch configurations on the plasticity of BMG structures by experimental method. Qu et al.1 investigated the notch tensile behavior of Zr-based BMGs, and found that the tensile strength of the BMGs is insensitive to notches, and notched BMGs Contributing Editor: Jörg F. Löffler a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.52 J. Mater. Res., Vol. 31, No. 6, Mar 28, 2016
exhibit enhanced plastic deformation ability with the formation of shear band zones. Wu et al.2 proposed the critical shear offset to explain the strong size effect on the enhanced plasticity of BMGs by taking account of the shear fracture energy density, and pointed out that the failure mode is very sensitive to the notch depth and notch sharpness. Zhao and Zhang3 performed the compressive tests on the Zr- and Ti
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