Mapping Static and Dynamic Crack-Tip Deformations Using Reflection-Mode Digital Gradient Sensing: Applications to Mode-I and Mixed-Mode Fracture

The reflection-mode digital gradient sensing (rDGS) 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 measuring small deflections of light rays. Here, for the first time, r-DGS is implemented to study both mode-I and mixed-mode (I/II) problems and evaluate fracture parameters. Under dynamic loading conditions, r-DGS is employed in conjunction with highspeed digital photography to map surface slopes in edge cracked plates subjected to one-point impact. The measured surface slopes are used to successfully evaluate instantaneous stress intensity factor histories by combining measurements with the corresponding asymptotic crack-tip fields and performing over-deterministic least-squares analyses. Finite element computations are also used to complement experimental measurements as needed.