Assessing Shot-Peening Residual Stresses by Using the Incremental Hole-Drilling Technique and Laser Interferometry (DSPI)

João P Nobre,Matias Viotti,Miguel Oliveira,Luís Coelho,Maria J Marques,António Castanhola Batista,Armando Albertazzi

doi:10.4028/www.scientific.net/amr.996.269

Abstract

The incremental hole-drilling technique was applied to determine residual stress profiles in shot-peened steel layers. The accuracy of using an enhanced Digital Speckle Pattern Interferometry technique for measuring the strain relaxation arising around the drilled holes and, consequently, the in-depth residual stress distribution induced by shot-peening, was evaluated. The experimental results were systematically compared with those determined using standard electric strain-gauges. The X-ray diffraction technique was chosen as reference due to its high accuracy to determine shot-peening residual stresses.

Highlights

The aim of this investigation was to perform a comparative analysis between two different techniques for measuring deformations, strain gauges and laser interferometry, to be applied with the incremental hole-drilling technique (IHD) to determine non-uniform residual stresses
The strain relaxations curves determine by Digital Speckle Pattern Interferometry (DSPI) are always below those determined by strain gauges (SG)
Since the residual stresses are related with the strain-depth gradients, it is possible to conclude that DSPI seems to underestimate the residual stress distribution existing in each shot-peened material

Summary

Introduction

The aim of this investigation was to perform a comparative analysis between two different techniques for measuring deformations, strain gauges and laser interferometry, to be applied with the incremental hole-drilling technique (IHD) to determine non-uniform residual stresses. This investigation was made through a partnership between the CFisUC of the University of Coimbra, Portugal, and the Labmetro of the Federal University of Santa Catarina, Brazil. Specific calibration functions are needed, since it is necessary to correlate the strain relaxation measured at the material's surface with the average stress existing in each depth increment These coefficients can be determined through a numerical calibration by using the finite element method (FEM). The first diffracted order is deflected towards a central circular area on the specimen and produces a double illuminated circular area of about 8 mm in diameter with radial sensitivity

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Experimental Results and Discussion

Conclusions