On the exploitation of multiple 3D full-field pulsed ESPI measurements in damage location assessment

The structural dynamics of a manufactured part or system is often used as a key player in the discrimination of a sound behaviour or of a defected component, which must not go into service. Many NDT approaches exploit different loading systems to enhance the recognition of defects in components. Among the NDT techniques, Shearography, with its opto-mechanical shearing of electronic speckle pattern interferometry fields, mainly uses the vacuum technology to give a distributed, but static, loading on the sensed surface. Instead, it was already demonstrated that broad frequency excitation can enhance the defects' recognition, as the higher structural dynamics may reveal local anisotropies that are not excited by static loading only, but need tonal signature in the testing deformation source. In this work the attention is drawn onto the concurrent exploitation of multiple 3D full-field data, obtained by pulsed ESPI displacement measurements with sound pressures and shaker mono-tonal excitations at different frequencies. The usage of multiple data allows to gather the information about different defects that are oddly revealed at single frequency lines. The 3D nature of the datasets plays a relevant role, as the inhomogeneities are more easily detected from the in-plane displacements. Before summing all the available information, the single datasets can be enhanced by thresholding and functionally grading the 3D displacements. The application of the proposed method on a FGRP honeycomb panel, defected on purpose by proper manufacturing, was able to reveal all the know discontinuities by clustered areas of high displacement amplitude, by means of the processed 3D full-field dynamic maps. (C) 2022 The Authors. Published by Elsevier B.V.