The effectiveness of optical (mostly interferometric) methods for the measurement of residual stresses is largely demonstrated in literature. Nevertheless, these techniques are still confined to optical laboratories due to their high sensitivity to vibrations which makes it very difficult to perform the measurement in an industrial environment.\ud
Digital Image Correlation (DIC) has recently been proposed as a possible solution to this problem: this\ud
non-interferometric technique is much less affected by vibrations, but its sensitivity is relatively low, thus negatively affecting the accuracy of results. \ud
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This work proposes to use a variant of Digital Image Correlation, known as Integrated DIC (iDIC), in combination with the hole drilling technique. Since iDIC directly incorporates in its formulation the displacement field related to hole drilling, it overcomes most of the problems of standard DIC; in this way it is possible to obtain accurate results without using interferometric techniques
The phase unwrapping problem consists in mingling out an integer field whose values make the original wrapped phase field continuous. Even if in principle the problem is very simple--a direct integration of the wrapped phase field suffices--in the presence of noise and/or undersampling, the solution is no longer unique and the direct integration methods usually fail to find an acceptable solution. This work presents what is to my knowledge a new unwrapping algorithm that attempts to find the solution by iteratively merging and shifting the continuous areas until a single region is built or no further moves are possible. Unlike the tile methods, the regions can have arbitrary shape and need not be ingle-connected so that, by removing the predefined size and shape constraint, the algorithm is very robust. The greater freedom of the regions' shape makes their handling more problematic, so that certain implementation aspects, critical to algorithm performance, are presented here. Some unwrapping examples are also presented and memory requirements are discussed.
Most of the full field methods for residual stress investigation combine an optical interferometric technique (grating interferometry, speckle interferometry, holographic interferometry) with the standard hole drilling method. Nowadays many articles describing this kind of approach exist, but most of them focus on the experimental aspects while little attention is devoted to the optimal usage of the huge mass of data that the optical methods make available. This paper, without relying on a specific experimental technique, focuses on the development of a new analytical method that attempts to consistently use all the available data. After a detailed algorithm description, the proposed analysis procedure is tested against numerically generated residual stress fields simulating in-plane speckle interferometry. The results obtained show the reliability and robustness of the algorithm.
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