1 MEASUREMENT OF RESIDUAL STRESSES WITH OPTICAL TECHNIQUES

The goal of this work is the development of other experimental techniques to measure residual stresses, as alternative to the hole-drilling method with strain gages. The proposed experimental techniques are based on the use of Moiré Interferometry and in-plane Electronic Speckle Pattern Interferometry (ESPI). Both are field techniques allowing the assessment of in-plane displacements without contact and high resolution. Grating replication techniques were developed to record high quality diffraction gratings onto the specimen’s surfaces. An optical set-up of laser interferometry was developed to generate the master grating (virtual). An in-plane ESPI set-up was also designed and implemented to measure displacements in one direction. The stress relaxation was promoted by the blind hole-drilling and the obtained fringe patterns (Moiré and speckle) were video recorded. Image processing techniques were applied to assess the in-plane strain field. A finite elements code (ANSYS®) was used to simulate the stresses relaxation process whose values were compared with the experimental data and to calculate the hole-drilling calibration constants