Improvement of stress analysis by digital image correlation and the intelligent hybrid method

Now, many methods of measuring the external force which acts on a structure have been devised. We developed the method that a stress and a strain could be analyzed in automatic, non-contact, and real time by combining digital image correlation and the intelligent hybrid method. However, it is not easy to evaluate the sub-pixel order displacement with high accuracy in digital image correlation. On the other hand, the displacement in a crack problem is a sub-pixel in many cases. Hence, we examined the algorithm for measuring the infinitesimal deformation and discussed which method raises accuracy. The Newton-Raphson method that takes deformation of the image itself into consideration in deformation analyses was adopted, and the deformation gradient was extended to higher order by Taylor expansion. In order to extend the flexibility of this system, we used steel and an aluminum alloy specimens in the experiment. Then, a stress intensity factor was able to be evaluated less than 1% of the error as compared with FEM.