Whole-field speckle strain sensor

The construction of a whole field speckle strain sensor is reported. The sensor makes use of the in-plane motion of defocused laser speckles in a telecentric imaging system. To distinguish between the contribution to the speckle motion from surface displacement, strain, rotation and tilt three different illumination directions were used. For illumination three pigtailed laser diodes of slightly differentwavelength was used. To allow for simultaneous acquisition of the three speckle patterns, the different wavelengths were splitted with the aid of dichroic mirrors and directed onto separate synchronised detectors. The motion of the three speckle patterns is calculated using digital speckle photography and combined to give the three in-plane components ofthe strain tensor. A discussion about sources ofrandom and systematic errors are included.