Comparison Between Surface and Near-Surface Residual Stress Measurement Techniques Using a Standard Four-Point-Bend Specimen

Background Determination of near-surface residual stresses is challenging for the available measurement techniques due to their limitations. These are often either beyond reach or associated with significant uncertainties. Objective This study describes a critical comparison between three methods of surface and near-surface residual stress measurements, including x-ray diffraction (XRD) and two incremental central hole-drilling techniques one based on strain-gauge rosette and the other based on electronic speckle pattern interferometry (ESPI). Methods These measurements were performed on standard four-point-bend beams of steel loaded to known nominal stresses, according to the ASTM standard. These were to evaluate the sensitivity of different techniques to the variation in the nominal stress, and their associated uncertainties. Results The XRD data showed very good correlations with the surface nominal stress, and with superb repeatability and small uncertainties. The results of the ESPI based hole-drilling technique were also in a good agreement with the XRD data and the expected nominal stress. However, those obtained by the strain gauge rosette based hole-drilling technique were not matching well with the data obtained by the other techniques nor with the nominal stress. This was found to be due to the generation of extensive compressive residual stress during surface preparation for strain gauge installation. Conclusion The ESPI method is proven to be the most suitable hole-drilling technique for measuring near-surface residual stresses within distances close to the surface that are beyond the penetration depth of x-ray and below the resolution of the strain gauge rosette based hole-drilling method.

Inverse Hole-Drilling Method for Residual Stress Investigation

The method for residual stress measurement using through the hole drilling and investigation of the residual stresses relief with the help of incremental layers removing is presented. Drilling the rosette-hole from the opposite side – the inverse layers removing – have to be used for evaluation of residual stress near the back side of the object wall in cases when this surface is inaccessible for any hole-drilling instrument. The strain gauge rosette is installed on the opposite side of the drilled wall and a new mechanical task of incremental layers removal must be solved. The calibration constants for residual stress evaluation of HBM RY21 type rosette for this case were derived using numerical modeling by FEA and its experimental verification.

Probabilistic Evaluation of Residual Stresses for Hole-Drilling Tests

The article focuses on the application of a probabilistic approach to the evaluation of residual stresses in tensometric (strain gauge) hole-drilling methods. The principle of this method is based on the use of a strain gauge rosette on the surface of the tested component and the subsequent drilling of a hole in the centre of this rosette. This disturbs the internal force and moment equilibrium, which in turn causes surface deformations that are measured by the rosette. The measured deformations are then evaluated, and derived theories are applied to determine the course and magnitude of residual stresses taking into account the random character of the input parameters using the SBRA (Simulation-Based Reliability Assessment) method, which proves to be highly practical. The probabilistic approach to determining residual stresses is a new, original approach which brings a suitable and accurate description of the variance in measured values.