Impact of strain rate on the Indentation Size Effect: Evidence of an intimate link between Size effect, Strain Rate and Ductility in Soda-lime Silica glass

Abstract

Many glasses exhibit the so-called indentation size effect (ISE), where the indentation hardness decreases with the maximum applied force. Here, we seek to uncover the connection between the ISE and strain rate in soda-lime silica (SLS) glass using micro-indentation. Two different loading protocols: constant loading rate (CLR), resulting in a nonlinear strain rate through the depth of indent, and a non-linear loading rate that gives a constant strain rate (CSR) with depth, are used to determine Hardness for six different strain rates and seven peak forces. A modified Bernhardt size effect law is then used to determine the extent of the ISE and load-independent hardness. We show that a small increase in micro-ductility, which can be achieved by either switching from a CLR to CSR protocol or by increasing the applied rates, can greatly reduce the extent of the ISE and slightly reduce the load-independent hardness.