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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 ( G d )-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 G d – 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. [ABSTRACT FROM AUTHOR]

In this paper, the dynamic crack-interface interactions and the related mechanics of crack penetration vs. branching at a weak interface are studied experimentally. The interface is oriented perpendicular to the incoming mode-I crack in an otherwise homogeneous bilayer. The focus of this investigation is on the effect of interface location and the associated crack-tip parameters within the bilayer on the mechanics of the ensuing fracture behavior based on the optical methodologies laid down in Ref. Sundaram and Tippur (2016). Time-resolved optical measurement of crack-tip deformations, velocity and stress intensity factor histories in different bilayer configurations is performed using Digital Gradient Sensing (DGS) technique in conjunction with high-speed photography. The results show that the crack path selection at the interface and subsequently the second layer are greatly affected by the location of the interface within the geometry. Using optically measured fracture parameters, the mechanics of crack penetration and branching are explained. Counter to the intuition, a dynamically growing mode-I approaching a weak interface at a lower velocity and stress intensity factor penetrates the interface whereas a higher velocity and stress intensity factor counterpart gets trapped by the interface producing branched daughter cracks until they kink out into the next layer. An interesting empirical observation based on measured crack-tip parameters for crack penetration and branching is also made. [ABSTRACT FROM AUTHOR]