Multipoint diffraction strain sensor: theory and results

TLDR: In this article, a multi-point diffraction strain sensor was developed using a moire interferometer with the added feature of whole-field strain determination, which was implemented by simultaneous tracking of sampled wavefront diffracted from the component under test.

Abstract: A multipoint diffraction strain sensor has been developed using a moire interferometer with the novel added feature of whole-field strain determination. This unique feature has been implemented by simultaneous tracking of sampled wavefront diffracted from the component under test. In this sensor a high-frequency diffraction grating is bonded on the specimen, which is illuminated by two symmetric collimated laser beams, as in a typical moire interferometer. The first orders of diffracted beams impinge on a CCD camera, via a microlens array. The lens array serves a dual purpose—to sample the diffracted wavefront and to focus the wavefront to a number of spots on the CCD. The deviation of the individual spots generated by both the beams is directly proportional to the normal strain and a component of the shear strain. Simultaneous strain measurement at more than a thousand points can be readily obtained and is demonstrated in this paper. This novel technique is expected to be very valuable in numerous industrial metrology applications.