Utilizing digital image correlation to determine stress intensity factors

There is a major concern with aging and fretting wear in the transportation industry. The presence of an edge crack in structures can be tolerated if its evolution is predicted using fracture mechanics. In this study, the digital image correlation (DIC) technique was employed to evaluate the in-plane stress intensity factors (SIFs), KI and KII, for the contact between a half plane with an edge crack and an asymmetric tilted wedge. DIC requires two digital images of the same sample at different stages of loading to measure the corresponding displacements and strain fields. A computer code was developed to process the captured images and determine the correlation coefficients. Fracture mechanics theory was then applied to calculate the SIFs from displacement fields obtained via DIC analysis. The effect of the wedge tip angle on the SIFs was studied using DIC. To highlight the advantages of DIC, a photoelasticity method was also employed to determine SIFs for the identical problem. The SIF values from the two techniques were compared and a good agreement was observed. In summary, it was shown that although the DIC method requires simple setup and minimal sample preparation relative to the alternatives, it provides reliable results.