Metrological justification of reflection hologram interferometry with respect to residual stresses determination by means of blind hole drilling

Abstract A description of practical implementing combined technique for residual stress determination in plane thick-walled structures is presented. The main features, which are inherent in a procedure of reconstruction and quantitative interpretation of fringe patterns arising as a result of blind hole drilling in residual stress field, are discussed in detail. Two plane aluminium specimens welded from two equal parts having dimensions 130×80 mm in-plane and thickness of 18 and 12 mm are the objects of investigation. Weld seam is performed along the shortest side of both specimens. A wide set of actual fringe patterns related to both uniform and non-uniform residual stress field is reconstructed. Most of typical fringe patterns are presented as illustrations. A whole set of available interferograms shows that a residual stress field in both thick-walled plane specimens investigated consists of both a uniform and non-uniform part. It is shown that a form of both non-uniform and uniform stress fields remains practically the same along the weld line. Moreover, non-uniform residual stress field at the proximity of weld seam is of similar form for both specimens. Emphasis is made in a choice of the transition model proceeding from a comparison of actual interferograms and reference fringe patterns. For the first time reference fringe patterns are constructed by using data obtained from corresponding actual fringe patterns, which reveal a non-coincidence between specimen's symmetry cross-sections and principal strain directions. It is shown that relations developed for a probe hole drilled in uniform 2-D stress field can be used for deriving residual stress components when fringe patterns obtained reveal a presence of local strain gradients. A good agreement between actual and reference fringe patterns is achieved in a case of local strain gradients existing. Comparing two types of interferograms related to uniform residual stress fields demonstrates their full coincidence. It is shown that the whole set of obtained fringe patterns consists of three main groups. The main evidence, which reveals an interferogram belonging to each specific class, is a typical form of fringes configuration. The main principles of creating the general fringe patterns catalogue are established and initial draft of this catalogue is developed. Distributions of residual stress components are constructed for different surfaces of both specimens under study. Quantitative results have a form that is typical for welded joints of structures bounded by plane surfaces. It is shown that fine nuances inherent in residual stress distributions over different specimen faces can be reliably derived from recorded fringe patterns of any type.