Elucidating the Mechanisms of Rate-Dependent Deformation at Ambient Temperatures in a Model Metallic Glass

• Main Author: Harris, Matthew Bradley
• Format: Others
• Published: BYU ScholarsArchive 2015
• Subjects: shear transformation zone; shear band; mesoscale; deformation; strain rate; metallic glass; flow serration; Mechanical Engineering
• Online Access: https://scholarsarchive.byu.edu/etd/6145; https://scholarsarchive.byu.edu/cgi/viewcontent.cgi?article=7145&context=etd

In this work, the Shear Transformation Zone (STZ) dynamics model is adapted to capture the transitions between different regimes of flow serration in the deformation map of metallic glass. This was accomplished by scaling the STZ volume with a log-linear fit to the strain rate, and also adjusting the activation energy of an STZ with a log-linear fit to maintain constant yield strength at differing strain rates. Twelve simulations are run at each of six different strain rates ranging from 10-5 to 100 s-1, and statistics are collected on simulation behavior and shear band nucleation and propagation rates. The simulations show shear band nucleation has a positive correlation to strain rate, and shear band propagation has a negative correlation to strain rate. This shows that in STZ dynamics, the regime of reduced flow serration arises due to competing rates of nucleation and propagation, supporting the hypothesis proposed by Schuh. A positive correlation between critical shear band nucleus size and strain rate is proposed as an underlying cause of these rate dependencies.