Residual stress determination and defect detection using electronic speckle pattern interferometry

Abstract

The paper deals with the methodology of determining residual stresses using Electronic Speckle Pattern Interferometry (ESPI). ESPI can be used as a truly non-destructive testing technique in that it is a laser based, optical, full field, non contacting method which reveals surface displacements to an accuracy of approximately 300 nanometres when a Helium Neon laser is used. In a simple experiment, a fixed-ends rectangular aluminium plate was subjected to uniform loading and the out of plane surface displacement field was obtained through ESPI. Subsequently a comparison of these measurements was made with measurements obtained after the plate was subjected to shot peening. The above method aimed to identify the extent of residual stresses that were imposed on the rectangular plate after the shot peening process which is known to induce such stress. Bearing in mind that ESPI produces a full field surface displacement map through a characteristic interference fringe pattern, any anomaly displayed on the fringe pattern could be interpreted as a flaw or defect on or beneath the surface under observation. The authors have included in this paper typical examples where the ESPI applied in a prototype device constructed by the authors, has identified defects in various engineering components made from a variety of materials.