Accurate Strain Distribution Measurement Based on the Sampling Moire Method

To obtain accurate measurement of non-uniform strains over the entire surface of materials or structures, in this study, the sampling moire method is applied to two-dimensional measurement of in-plane displacement and strain distributions. The two-dimensional displacement distribution is obtained by detecting the phase difference of the moire fringes, and the strain distribution is determined by measuring the change of grating pitches on the specimen in vertical and horizontal directions before and after deformations. A compensation technique of fringe order is proposed to eliminate the pitch error of fabricated grating. In addition, a spatial filtering procedure in phase distribution is suggested to reduce the random measurement error. The deformations of an aluminum specimen with a through hole under different tensile loads were measured by the proposed method. Experimental results indicated that the measurement accuracy of strain distribution can be dramatically improved by combination the above-mentioned two techniques. This method is useful to evaluate mechanical properties of various materials under tension/compression or heating/cooling testing.