Low-cost speckle interferometry for measuring 3D deformation fields: Hardware and software

In the present paper the authors propose a portable and low-cost speckle interferometer for evaluating 3D deformation fields. The interferometer was designed and realized with the aim of carrying out measurements on small areas, hence it can be used to approach problems characterized by displacement field with highly localized gradients, such as the strain relief occurring in residual stress evaluation or the displacements which arise around notches or crack tips. The costs of the experimental equipment were reduced by employing laser diodes as light sources, a PZT actuator designed and calibrated by the authors and a control electronics realized on purpose. Moreover the configuration which was adopted allows further saving on optical components. The experimental results reported at the end of the paper, and obtained by a specimen subjected to 3D rigid body motions, show a high repeatability and accuracy. Furthermore the experimental results have shown that the geometry of the optical setup implies the variation of the sensitivity vectors on the inspected area, but this effect can be evaluated (analytically and/or experimentally) and taken into account in order to increase the accuracy of the measurements.