Residual stress estimation based on 3D DIC displacement filed measurement around drilled holes

Residual stress might influence noticeably fatigue strength and fracture behavior of materials, therefore accurate methods of its determination are desired. The most popular method up today is based on strain measurements resulted from material relaxation near the drilled hole. Tensometric rosettes of defined geometry are used for strain measurements in 3 or 6 positions around the hole. The method has some drawbacks related to its sensitivity to hole and rosette centers eccentricity, averaging strain from tensometers area, time consuming rosettes fixing procedures and calculations based on only a few strain readings. Tensometric rosettes might be replaced by non-contact optical displacement fields measurements by means of Digital Image Correlation (DIC) giving much more information (hundreds or thousands of data points) for residual stress calculations. In the paper results of experiments concerning 3D DIC measurements usage for displacement field determination near the drilled hole in preloaded steel samples which afterwards were used as input data in the iterative procedure for the analytical model parameters fitting are presented. Details of testing stand allowing precise hole drilling without need of cameras used for DIC measurements movement during the drilling process and algorithm for inverse method calculations are described. Additionally, FEM model developed for introducing correction terms for blind hole case to the analytical model existing only for through hole instance is discussed.