Dynamic fracture of soda-lime glass: A full-field optical investigation of crack initiation, propagation and branching

Dynamic crack initiation, growth and branching phenomena are comprehensively investigated in soda-lime glass using a vision-based method, Digital Gradient Sensing (DGS), in conjunction with digital ultrahigh-speed photography. Being a high-stiffness and low-toughness structural material, soda-lime glass poses enormous temporal and spatial challenges to opto-mechanical measurements using legacy techniques. Unlike the past works on indirect evaluation of instantaneous stress intensity factors in glass via crack speed, DGS is capable of direct quantification of both crack-tip fields and crack speeds. This is useful for examining the dynamic fracture characteristics such as pre- and post-crack initiation histories, crack initiation toughness, energy release rate (Gd)-apparent velocity (V) variation, and to shed light on crack bifurcation phenomenon. Accordingly, directly measured mixed-mode stress intensity factor histories and crack-tip velocity histories at branching and subsequent growth are reported. These are supplemented with Gd-V plots which show certain unique signatures at branching. From the measured fracture parameters, a material length characteristic based on microcracking due to normal stress in the crack growth direction ahead of the propagating crack that triggers branching is advanced.