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Transparent brittle ceramics such as soda-lime glass pose unique challenges for performing full-field optical measurement of deformations and stresses to characterize fracture and failure behaviors. Low fracture toughness coupled with high stiffness and elastic wave speeds are among the factors responsible for some of these challenges as deformations tend to be small and confined to an extremely small region near the stress concentrators. Need for strong birefringence, elaborate optics, or lack of sufficient measurement sensitivity are some of the factors against legacy techniques such as photoelasticity, optical interferometry, and speckle methods, respectively, to study soda-lime glass. Motivated by these factors, the feasibility of Digital Gradient Sensing ( DGS) method to measure crack-tip and contact-induced deformations in soda-lime glass under quasi-static loading is demonstrated. This first of a two parts paper demonstrates the applicability of DGS for the problem under quasi-static loading condition. The optical measurements are used to evaluate the relevant parameters and compare with the analytical solutions. The second part of this study is focused on measuring contact-point and crack-tip deformations during impact-induced stress wave loading. [ABSTRACT FROM AUTHOR]

Transparent brittle ceramics such as soda-lime glass pose unique challenges for performing full-field optical measurement of deformations and stresses to characterize fracture and failure behaviors. Low fracture toughness coupled with high stiffness and elastic wave speeds are among the factors responsible for some of these challenges as deformations tend to be confined to an extremely small region near an almost mathematically sharp growing crack. Need for strong birefringence, elaborate optics, or lack of sufficient measurement sensitivity are some of the factors against legacy techniques such as photoelasticity, optical interferometry, and speckle methods, respectively, to study soda-lime glass. Motivated by these factors, the feasibility of digital gradient sensing ( DGS) method to measure impact induced deformations near a contact-point and a dynamically growing crack-tip in soda-lime glass are demonstrated in this work. This second of a two-part paper demonstrates the applicability of DGS for the problems under stress wave loading conditions. Ultrahigh-speed photography (1 million frames per sec) in conjunction with DGS and a Hopkinson pressure bar to load soda-lime glass specimens are employed. The optical measurements are postprocessed to obtain relevant engineering parameters and stress field [ABSTRACT FROM AUTHOR]

Mixed-mode dynamic crack initiation and growth in polymethymethacrylate (PMMA) and polycarbonate (PC) are studied experimentally. A simple specimen geometry in conjunction with a dynamic loading configuration to generate different mode-mixities at crack initiation is demonstrated. A Hopkinson pressure bar is used to rapidly load free-standing edge cracked samples in a reverse impact configuration. By eccentrically loading the specimen relative to the crack line, various mode-mixities at crack initiation are achieved by increasing the initial crack length while keeping all other experimental parameters the same. A relatively new full-field optical technique, Digital Gradient Sensing (DGS), along with high-speed photography is used to perform full-field measurements. DGS measures instantaneous angular deflections of light rays representing two orthogonal stress gradients under plane stress conditions. The mode-I and -II stress intensity factor histories are evaluated via over-deterministic least-squares analysis of optically measured data. By quantifying the critical stress intensity factors evaluated at crack initiation, dynamic fracture envelopes are developed for both the polymers. The results are studied comparatively and relative to the brittle fracture criteria. From measured stress intensity factors and crack speeds in the post-initiation regime, energy release rate vs. velocity plots for different mixed-mode configurations are produced for both the polymers. [ABSTRACT FROM AUTHOR]