Abstract

A new method for measuring the principal residual stresses on the surface of a thin metallic specimen is presented. The novelty of the method resides in a combination of the layer removal technique by chemical etching and of electronic speckle pattern interferometry to measure the ensuing deformation. It is shown that the loci of constant deflection with respect to the original plane surface are conic sections. An interferometer sensitive to out-of-plane displacements was used, yielding fringe patterns that reproduced those curves. Immediate visualization of the orientation and relative magnitude of the principal stresses within the removed layer was then possible. A fit of the measured deformation to the theoretical shape, together with knowledge of the initial and final thickness of the specimen and of the elastic properties of the material (a cold-rolled low-carbon steel sheet), allowed estimating the principal stresses. It is shown that the critical factor that determines the uncertainty of these estimates is the thickness of the removed layer. © 2009 IOP Publishing Ltd.