Digital shearography for strain measurement: an analysis of measuring errors

Recently, the digital shearography, a combination between the laser optical measurement and the digital image processing, has been developed as an industrial measuring method for strain measurement. With the support of the digital image processing, the flexural strains ((delta) 2w/(delta) x2, (delta) 2w/(delta) y2 and (delta) 2w/(delta) x (delta) y) can be determined by using one illuminating beam. The inplane strains ((delta) u/(delta) x, (delta) v/(delta) y, (delta) u/(delta) y and (delta) v/(delta) x) can also be measured using two alternate illuminating beams. However, a detailed analysis of measuring precision using the shearographic strain measurement method has not been reported. This paper will focus on the analysis of the factors which influence the measuring accuracy, such as the shearing amount, the sensitivity vector, the errors of phase shifting, the relatively large rigid body motion etc. The relationship between these factors and the measuring precision are presented.