Elastic-plastic stress analysis near the crack tip by the 2-dimensional elastic-plastic hybrid method and digital image correlation

In a previous study, the authors have developed the intelligent hybrid method for 2-D elastic stress analysis. In this study, we have analyzed about the elastic-plastic singular stress field near the crack tip by digital image correlation and the elastic-plastic intelligent hybrid method. The surface images of an object before and after the deformation were taken by a CMOS camera. From these images, the displacement data corresponding to the 2-D mesh pattern were calculated by digital image correlation. The displacement data obtained from the experiment were including large error, so it is difficult to evaluate the stress and the strain with high accuracy using raw displacement data. Therefore, displacement data were smoothed by 2-D FFT filtering and the least squares method. After that we applied the elastic-plastic intelligent hybrid method proposed by Nishioka et al. Evaluation of the stress and strain fields and a fracture mechanics parameter can be carried out by this. In the experiment, the mode I loading was applied to CT specimen with a fatigue crack, and the image near the fatigue crack-tip in an elastic-plastic deformation process was taken by the CMOS camera. The speckle pattern on a specimen surface was made using five kinds of colour sprays. The 3-D finite element method was performed about the same specimen as the experiment, and the validity of this approach was discussed from the comparison of the experiment and 3-D finite element method.