Cascading crack bifurcations in soda-lime glass: Quantification of fracture mechanics-based precursors using Digital Gradient Sensing

Abstract

Dynamic crack growth in high-stiffness and ultralow-toughness amorphous materials such as soda-lime glass (SLG) often involves seemingly unprovoked crack branching events which are yet to be fully explained. The absence of optical tools for performing mechanical field measurements at sufficiently high spatial and temporal resolutions to decipher highly localized deformations at the tip of a crack growing in excess of mile-a-second speed has perpetuated this knowledge gap. The full-field method of Digital Gradient Sensing (DGS) used in conjunction with ultrahigh-speed photography has overcome some of these limitations allowing direct quantification of fracture parameters associated with different phases of crack growth in SLG (Sundaram and Tippur, 2018; Dondeti and Tippur, 2020). In this work, time-resolved stress gradients are measured in SLG plates of two different geometries, first one producing a single crack bifurcation event and the second two-tier cascading crack bifurcations, during dynamic wedge-loading experiments. The measurements are then used along with the asymptotic crack-tip fields to extract fracture parameters and identify crack branching precursors based on crack velocity, stress intensity factors, and higher order coefficients. The fracture surface roughness and other features are also separately quantified via high-resolution post-mortem examination to corroborate them with the optically measured quantities.