Full field residual stress determination using hole-drilling and electronic speckle pattern interferometry (ESPI) with phase unwrapping method

J.N Aoh,B.I Lyu

doi:10.1051/epjconf/20100610001

Abstract

The hole-drilling strain gauge technique has become a standard method in measuring residual stresses [1]. Moiré interferometry combining hole-drilling method opens additional opportunity for full-field residual stress measurement using optical interferometry [2]. The optical moiré method has a non-contact feature comparing with strain gauge method. Yet Moiré interferometry suffers a drawback in its complicated grating preparation on one hand and it is difficult to be applied to work piece with complicated geometry on the other hand. Electronic speckle pattern interferometry (ESPI) provides information about the displacement field of a surface and it can be conveniently used on asreceived surfaces without special surface preparation and can be applied to work piece with complicated geometry that may be unsuitable for applying strain gauge or gratings. Studies on combining ESPI with hole-drilling show that is feasible to obtain reasonable residual stress values [3, 4]. The purpose of this study was to demonstrate the detail of hole-drilling technique combining ESPI with phase unwrapping method to reveal the full field stress distribution and to measure the associated stress field on a thin specimen exerted by a uni-axial load. This study also demonstrates the noise reduction achieved by Gaussian low pass filter and a successful phase unwrapping resulted from five-step phase shifting and cellular automata method.

Highlights

The light from a laser source is split into two beams
One split beam emerges from a PZT-stage to provide stepwise phase shifting and it further interferes with the other split image beam on the specimen surface to produce speckle patterns onto the CCD camera
The continuous phase maps were reconstructed with higher quality and lower noise by applying the Schmitt’s five-step phase shifting algorithm and cellular automata (CA) phase unwrapping method

Summary

Introduction

The light from a laser source is split into two beams. One split beam emerges from a PZT-stage to provide stepwise phase shifting and it further interferes with the other split image beam on the specimen surface to produce speckle patterns onto the CCD camera. By recording the speckle images of stepwise phase shifting before and after hole-drilling, the fringe patterns at each step can be obtained.

Objectives

Results

Conclusion