Technology and Equipment for Determination of Residual Stresses in Welded Structures Based on the Application of Electron Speckle-Interferometry

Abstract

The technology and equipment for determination of residual stresses in the welded structures, using electron speckle-interferometry combined with the hole-drilling method (ESPI-HD), have been described. A special new approach to the conventional method of speckle-interferometry to investigate the stress gradients over the test object surface has been added. The developed equipment has been applied for determination of residual stresses in the different structures: the gas-turbine rotor, the welded shell and the structural elements with the large grain size.

Residual Stresses Determination with Plasticity Effects by Electron Speckle-Interferometry Hole-Drilling Method

“…The displacement curve ( ) calculated using elasto-plastic model is similar to the curve ( ), that received at linear-elastic model (Fig.4, a). However, derivatives ∆ ∆ ⁄ (Fig.4.b) calculated under the assumption of linear elastic and elasto-plastic behavior of the material, show that at the angles in the range [0, 6 ⁄ ] the curves ∆ ∆ ⁄ and ∆ ∆ ⁄ are practically identical, and the greatest deviations are observed at = 3 ⁄ . It can be concluded from this graph that the plastic deformations make the greatest influence on the displacements of surface points around the hole for the angles in the range…”

“…In the paper [3] the use of a fourelement strain-gauge rosette has been considered to find "effect of plasticity" and real values of RS. Another extension of the hole drilling method is application of a non-contact speckle-interferometry technique to measure displacements around the hole [4][5][6]. The ESPI-HD method possesses such an important advantage as possibility of displacement data obtaining at a large amount of points near the hole.…”

Application of Local Current Pulses for Determination and Control of Residual Stresses

“…In recent works other researchers also used holographic interferometry [5][6][7]. The progress of computer engineering allowed developing high-efficient methods for residual stresses determination using electron speckle-interferometry (ESPI) and blind hole drilling [8][9][10]. They provide sufficiently wide opportunities for revealing local features of residual stress distribution.…”

“…The data of the displacements, measured in the points along the circle with diameter AB (Fig. 2, a) and located at a certain distance (2.5r0) from the center of the drilled hole of radius r0, are used for determination of residual stresses using derived formula [10]. a) b) Fig.…”

“…The electron speckle-interferometry in the combination with the hole-drilling method can be used for fast and accurate determination of residual stresses [9,10]. The ESPI method for residual stresses determination is based on the application of the optical scheme of the speckleinterferometer in which the investigated object section is illuminated under the same angle symmetrically from two directions, so that it is possible to determine the in-plane components of the displacement vector, which characterize the deformation of the object.…”