1. Reflection-Mode Digital Gradient Sensing Technique for Experimental Fracture Mechanics

In this work, the reflection-mode Digital Gradient Sensing (r-DGS) method is extended for visualizing and quantifying crack-tip deformations in solids under quasi-static and dynamic loading conditions. The r-DGS technique employs digital image correlation principles to quantify two orthogonal surface slopes simultaneously in specularly reflective solids by quantifying small deflections of light rays. For the first time, r-DGS has been implemented here to study both mode-I and mixed-mode (I/II) problems and quantify fracture parameters. Under dynamic loading conditions, r-DGS is implemented in conjunction with high-speed digital photography to map surface slopes in edge cracked plates subjected to one-point impact. The measured surface slopes have been used to successfully evaluate stress intensity factor histories by pairing measurements with the corresponding asymptotic crack tip field descriptions using overdeterministic least-squares analyses.