Measurement of Residual Stresses with Optical Techniques

Abstract

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.

Moiré Interferometry Assessement of Residual Stress Variation in Depth on a Shot Peened Surface

“…The validation of these results was carried out and was presented by Ribeiro et al. [24]. One example of the measurements performed is presented in Figure 5.…”

Residual Stress Determination by Hole Drilling Combined with Optical Methods

“…12. In 2009, Ribeiro et al [90] reported the results of a comparative study of ESPI and Moire interferometric methods applied with hole drilling to find residual stresses. For both approaches, worst case discrepancies with known stresses were approximately 15%, with most discrepancies on the order of 5%.…”

Optical Sensor Developments for Measuring the Surface Strains in Prestressed Concrete Members

“…The optical speckle technique has evolved into a powerful tool for the measurement of surface strains since digital signal processing hardware and software have become widely available nowadays [3, 4, 5, 6]. It has the advantage that virtually no surface preparation is required, it works well for various surface structures and roughness and has high resolution [7, 8, 9].…”