Digital gradient sensing and analysis of dynamic crack stability, propagation, and branching

Understanding the underlying mechanisms of fracture mechanics plays a critical role in engineering design and analysis. This work investigates aspects of dynamic fracture and the transition from stable to unstable crack propagation by employing the digital gradient sensing method in conjunction with high-speed photography. Both quasi-static and dynamic loading scenarios are evaluated. Furthermore, the micromechanical fracture mechanisms are evaluated using optical microscopy and optical profilometry. Significant insights are gained regarding the relationship between loading, crack branching, and the micromechanical mechanisms that govern dynamic fracture. Differences between two models for formation of crack surface patterns, based on crack front waves and Wallner lines, are examined. Most interestingly, insights developed with respect to crack branching phenomenon, and its speed past branching have significant impact on the modeling of crack branching and dynamic fracture. Discovery of constant crack branch speed will require additional study of energy release rates associated with branching cracks