Examination of Accuracy of the Singular Stress Field Near a Crack-Tip by Digital Image Correlation

Displacements obtained experimentally normally are including errors that make it impossible to extract stresses strains with high accuracy using the raw displacement data. In the infinitesimal deformation within the elastic region of a steel or an aluminum alloy, the quantity of displacement is less than 1 pixel, and analysis accuracy deteriorates. We have developed a system which employs the 2-D intelligent hybrid method and can analyze the displacement more exactly in the sub-pixel field. By using the Newton-Raphson method in conjunction with 2nd order deformation gradients, it is demonstrated that this method can accurately extract stress intensity factors from a set of measured displacements.