Sensitivity Analysis of i-DIC Approach for Residual Stress Measurement in Orthotropic Materials

Measuring residual stress in orthotropic materials is significantly more difficult than in isotropic materials. Indeed, in addition to the usual technical problems, several new points have to be taken into account, e.g. the accurate identification of material principal directions and the thickness of the laminae, (assuming we are dealing with composite materials). Recently, a new approach to residual stress measurement in orthotropic materials has been proposed: it is based on the use of problem-specific displacement functions in the measuring loop of a Digital Image Correlation code. This is an elegant and effective solution because it allows for direct measurement of residual stress without the intermediate estimation of the displacement field. This work attempts to analyze the sensitivity of the new methodology to some of its controlling parameters such as the location of the center of the hole, the estimation of its radius and the identification of material parameters. By using synthetic images, all parameters and stress components are exactly known, thus a statistical analysis is possible and allows identification of the most critical ones, together with the required accuracy for reliable estimation of stress levels.