Quantitative in situ studies of dynamic fracture in a lithium metasilicate glass-ceramic by x-ray phase contrast imaging

Glass-ceramics are produced through controlled crystallization of base glass, with many of their properties depending on the specific microstructures. With respect to their mechanical properties, although this dependence has been widely studied under quasi-static loading conditions, limited studies have been carried out beyond the quasi-static regime, especially in the context of fracture. Here, we study the fracture of lithium metasilicate glass-ceramics having different microstructures but nominally identical mechanical properties, under dynamic three-point-bend loading conditions. Using time-resolved x-ray phase contrast imaging, we capture crack initiation and propagation in glass-ceramics specimens and quantify the crack tip speed evolution. We find that the crack speed differs for specimens possessing different microstructures, an observation that cannot be captured by linear elastic fracture mechanics theory via a standard homogenization modeling procedure. Postmortem characterizations of fracture surfaces aided by scanning electron microscopy and white light interferometry reveal strong crack-crystal interactions (e.g., trans-granular fracture) and identify a correlation between a lower crack speed and an increased roughness of the fracture surface. Our work demonstrates microstructure-modulated fracture behavior in glass-ceramics and brings up the scale interplay between material heterogeneity and homogenization in the context of modeling fracture in heterogeneous materials.