Evaluation of Stress-Intensity Factor of Mixed-Mode Crack by Hybrid Speckle Photography

The experiment was conducted on the compact normal and shear (CNS) specimens made of homogeneous and dissimilar materials subjected to mixed-mode loading. Many Young’s fringes patterns around the crack tip were taken and analyzed by the image-processing system developed in my laboratory. The displacement obtained by speckle photography is not as smooth as that obtained by the finite element analysis (FEA). Therefore, the displacement data were smoothed by 2 D FFT filtering and least squares method. The intelligent hybrid method proposed by Nishioka et al. was applied to the stress-strain analysis. Consequently, the stress and strain near the crack tip can be evaluated with high accuracy by the present stress-analyzing system. Then, the stress-intensity factor was evaluated by the virtual crack extension method (VCEM) and displacement extrapolation. The accuracy of stress-intensity factor at the free surface was discussed from both viewpoint of experiment and 3 D FEA.