Dynamic fracture of soda-lime glass plates studied using two modified Digital Gradient Sensing techniques

Abstract

Two modified full-field Digital Gradient Sensing (DGS) methods of higher measurement sensitivity, transmission-reflection DGS (tr-DGS) and double-transmission DGS (t2-DGS), are extended in this work to examine their feasibility to study fast fracture events in soda-lime glass by measuring stress gradients. Full-field optical measurement of deformations and stresses in such high-stiffness and low-toughness brittle material is very challenging. Extremely high crack speeds (~1400 m/s), low failure strain (εf < 0.1%), and highly localized sub-micron scale deformations are among the challenges to overcome in this material system to succeed in this regard. The higher measurement sensitivity of tr-DGS and t2-DGS make them particularly suitable for studying transparent glasses and ceramics relative to previous versions of DGS method. These two new methods are demonstrated for studying dynamically growing cracks in soda-lime glass plates subjected to dynamic impact loading in a modified Hopkinson pressure bar device and ultrahigh-speed photography (1 million fps). Previously proposed reflection DGS (r-DGS) is also implemented to comparatively show the benefits of higher measurement sensitivity offered by tr-DGS and t2-DGS methods. The measured stress gradients are numerically integrated to estimate σxx+σyy stress fields around the crack tip vicinity. The optical measurements are also used to obtain fracture parameter histories of crack speed, stress intensity factors and energy release rates under mode-I conditions. The energy release rates increase rapidly when the crack speed approaches ~1400 m/s. The measured fracture parameters are also assessed using a complementary elasto-dynamic finite element model up to crack initiation. The agreement between measurements and simulations supports the feasibility of these two optical methods for studying dynamic fracture mechanics of this challenging material.