On the Use of iDIC (Integrated Digital Image Correlation) for the Slitting Method

The slitting method is a well-known technique for residual stress measurement. It consists of cutting a slot in the specimen while monitoring the relieved strains with one or more strain gauges. The stress distribution is then computed by solving a reverse problem. The use of Digital Image Correlation to replace the standard strain-gauge-based approach has been proven successful in previous work. In this new contribution, the authors want to explore the integrated Digital Image Correlation (iDIC) potential as a direct replacement for the entire procedure. Instead of using DIC as an optical extensometer—i.e., using a large DIC subset to extract single-point data—in the iDIC formulation, the shape functions describing the surface displacement field satisfy the equilibrium conditions. Thus, the minimization parameters (both in space and in time) are the Legendre polynomial weights directly connected to the residual stress values. To verify the new approach, an aluminum beam is loaded in bending above the yield stress and then unloaded using a four-point configuration; then, the slot is performed using a milling machine while imaging the back face. The use of strain gauges allows comparing the results of the new approach with the standard one.