Carrier fringe method of moiré interferometry for tiny strain measurements in micro-field

Abstract

In this paper, we demonstrate a new optical method for tiny strain measurements based on the principle of carrier fringes of moiré interferometry. A cross-line grating with frequency of 1200 lp/mm is replicated on the specimen surface, and the strain can be deduced from the changes in carrier fringes before and after the deformation of an object. Four coherent laser beams are used to obtain the carrier fringe patterns of field U and V . Both theoretical analysis and numerical simulation indicate that the ideal accuracy of strain can be controlled within a range of ±1µε. Case study of a plane extension experiment shows that the measurement accuracy of strain can be controlled within the range of ±10µε. The average strain values of every row of field U and every column of field V can be obtained by using this method, and approximated strain of every pixel in the whole-field can be further acquired, and thus it is possible to measure tiny strains occurred in a micro-field. The technology in this paper can provide comprehensive information for analyzing related mechanical content in the field of MEMS.