Residual stresses determination with plasticity effects by electron speckle-interferometry hole-drilling method

The electron speckle-interferometry hole-drilling (ESPI-HD) method for determination of residual stresses (RS) is based on drilling of a blind hole with a diameter of 0.5-1.0 mm and calculating stresses using displacements data measured by a speckle-interferometer. According to the standard procedure, calculations are made under the assumption of linear elastic behavior of the material. However, if the RS level is high, then plastic deformations caused by the stress concentration induced by the hole could lead to a stress calculation error. Unlike strain-gage hole-drilling (SG-HD) method which records strains only by three (six) strain gauges and elaborates in order to find the RS, the ESPI-HD method allows taking into account the displacements data at all points of the surface around the hole. Analysis of the displacements' variation across the circumference around the hole reveals local features related with plastic deformations. In this paper, a new approach for determination of RS by the hole drilling method that considers the plastic deformations has been proposed. This approach assumes determination of the plasticity effect by calculating stresses using displacements data at various sectors relative to the hole. Analysis of stresses variations calculated using values of displacements at different sectors allows retrieving the real stress state. (author)