A Method to Eliminate Measurement Error Caused by Residual Strain of Grating in Moire Interferometry

Abstract

Moire interferometry is a very sensitive optical method to measure the in-plane displacement of a solid specimen, and is useful to measure small deformation of solids. But, there often appears measurement error caused by the residual strain of the grating that is pasted on a specimen in Moire interferometry. The present paper applies Moire interferometry to the measurement of opening displacement of a notch in a plate specimen, and proposes a method to eliminate the error brought by the residual strain of the grating. The proposed method measures the change of the order of Moire interference fringes with varying the tensile force applied to the specimen, and obtain the residual displacement of the grating and the true opening displacement of the notch. The experimental results show that the opening displacement given by the proposed method is proportional to the square root of the distance from the notch tip. This fact says that the proposed method is successful in eliminating the measurement error caused by the residual strain of grating, and can measure the true COD without any phase-shifting methods.