Residual stress determination by optical interferometric measurements of hole diameter increments

The main questions, related to the residual stresses determination in thin welded plates by the general approach, are considered. The values of hole diameter increments in principal stress directions, obtained by both reflection hologram interferometry and electronic speckle-pattern interferometry, serve as the initial experimental information. The analytical basis shows that the formulae, which connect experimental data with residual stress components, represent unequivocally solution of the properly posed inverse problem. Simultaneous measurements of the local deformation response on the opposite faces of thin-walled object under study, when a single probe hole is drilled, is the essential condition of the general approach implementing. To do this, an optical system of combined interferometer is developed. The main feature of this optical set-up resides in a capability of simultaneous recording fringe patterns inherent in electronic speckle-pattern interferometry (ESPI) and reflection hologram interferometry on opposite specimen faces for the same through hole. The accuracy of the proposed method with respect to the residual stress components determination has been assessed by three different ways. It is shown that ESPI based interference fringe patterns of high density provides a fast and reliable way of determining residual stress values of the order 160-180 MPa at the weld seam proximity. Residual stress evolution due to cyclic loading is described through the use of ESPI data.