Reflection hologram interferometry combined with hole drilling technique as an effective tool for residual stresses fields investigation in thin-walled structures

Abstract

A detailed description of unconventional two-step technique of residual stresses determination is presented. This technique has the highest possible sensitivity with respect to plane residual stress components compared with all other destructive mechanical methods. The first step is a high-precision measurement of in-plane displacement components describing a distortion of drilled hole in principal strain directions due to residual stresses redistribution. The second stage is a choice of the most reliable transition model that is capable of deriving accurate residual stresses values from holographic interferometry data. A full metrological justification of both steps is established. Specific approach to a quantitative interpretation of fringe patterns arising near probe hole in terms of absolute fringe order difference is proposed and effectively implemented. Basic relations that allow us a quantitative determination of residual stress components are derived. A wide series of high-quality actual fringe patterns inherent in the procedure involved is obtained. Sophisticated technique for reference fringe patterns constructing is developed and implemented in order to carefully estimate and verify an accuracy of results obtained. A capability of the developed technique is demonstrated in the course of residual stress fields determination at the proximity of welded joints of thin aluminium specimens. Residual stress distributions corresponding to four different welding technologies are presented. An excellent correlation between most of the actual and numerically simulated fringe patterns is demonstrated for different types of residual stress state. It is shown how residual stresses of high level up to 200 MPa in aluminium alloy can be measured by means of the technique developed.