Digital Shearography: New Developments and Applications

Abstract

The main applications of temporal phase shift shearography are in NDT and strain measurement. Temporal Phase Shift Shearography for NDTThe most important application of temporal phase shift shearography, called digital shearography for simplicity, is for NDT, which enables flaws in objects/ materials to be found without damaging them. Compared to conventional NDT methods, such as ultrasonic, radiographic, magnetic article, dye penetrant, eddy current, and acoustic emission methods, digital shearography has the advantages of full-field measurement, high sensitivity, easy visualization, quick measurement speed, and real-time display of test results. Due to these distinct advantages, digital shearography has been widely accepted by the automotive and aerospace industries as a recommended NDT method for rubber and composite materials.1-2 The details of digital shearography for NDT have been described and discussed in Refs. 3 and 4. In this section, potentials and limitations of temporal phase shift shearography for NDT are reviewed, practical applications using different loading methods are demonstrated, and a few recent developments, such as NDT for testing relatively large objects and for measuring mirror-like surfaces, are presented and discussed.

Non-destructive testing and evaluation of composite materials/structures: A state-of-the-art review

“…Terahertz (THz)-based NDT technology has become a promising technique for composite inspection within last decade [46,47]. Research papers on the shearography technique is low, but it was promoted significantly by the invention of the laser in the 1960s [48], thus it is wellestablished and widely used for industrial NDT, especially in aerospace [49,50]. Although neutron imaging shares similar principles to X-ray imaging, the generation of neutrons is more expensive than for X-rays, the former requiring either a nuclear reactor or spallation process [51].…”

EXTREME shearography: development of a high-speed shearography instrument for measurements of the surface strain components during an impact event

“…The main limitation of two frames per camera can be overcome by increasing the number of cameras or by repeating the experiments with controlled delays 39 . The shearography configuration with spatial shifting 40 and the corresponding data processing flow is presented in Figure 2. When the object surface is deformed, the change of the optical paths in the reference and sheared field of views causes a change of the phase φ ∆ x at the camera, which can be extracted from complex amplitudes of the recorded interferograms.…”

Analysis of thermal strains and stresses in heated fibre metal laminates

“…Shearography theory and the principle of its operation as an NDI technique are well described in literature. [23,[27][28][29] Figure 4 shows the developed multicomponent shearography instrument with its multiple viewing and single illumination configuration. [30][31][32] A multicomponent configuration with three viewing directions was used to isolate the surface strain components (∂u/∂x, ∂v/∂x, and ∂w/∂x) for the shear in x-direction and (∂u/∂y, ∂v/∂y, and ∂w/∂y) for the shear in the y-direction, where u, v, and w are surface displacements along x, y, and z, respectively.…”

“…The measurement principle is based on a correlation analysis of interferometric speckle patterns captured before and after the surface deformation. Shearography theory and the principle of its operation as an NDI technique are well described in literature . Figure shows the developed multicomponent shearography instrument with its multiple viewing and single illumination configuration .…”