Multipoint diffraction strain sensor: an add-on to moiré interferometer

Multipoint Diffraction Strain Sensor has been developed based on a normal moire interferometer, with the novel feature of whole field strain determination, along with the possibility of rotation and tilt 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 of 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. This novel technique is expected to be very valuable in numerous industrial metrology applications.