Residual Stresses Measurement by the Hole-Drilling Technique and DSPI Using the Integral Method with Displacement Coefficients

The authors developed a portable optical residual stresses measurement device that combines the incremental hole-drilling method with digital speckle pattern interferometry working in polar coordinates. The device is able to measure radial in-plane displacement components around the drilled hole. A set of normalized radial displacement vectors are computed by the Finite Element Method for each hole depth increment, according to the integral method. The radial displacement field around the drilled hole is optically measured and data processed to extract the zero and second order harmonics and fitted by least squares method to the FEM coefficient vectors to quantify the amount of residual stresses in each material layer. The residual stresses profile is then determined for every 0.05 mm. A controlled experiment using a bent plate is used to experimentally evaluate the measurement performance of the developed approach. The results uncertainty are comparable to the strain gauge measurements.