Digital Shearography for Non-Destructive Evaluation

Digital shearography is an optical interferometric technique that measures surface strain by comparing two speckle patterns displaced laterally relative to one another. By analysing the phase difference between these patterns, minute deformations arising from subsurface defects, delaminations or inclusions can be visualised as fringe or phase‐map distributions. Unlike traditional ultrasonic or radiographic methods, shearography offers full‐field, non‐contact inspection, high sensitivity to strain gradients and robustness against environmental vibrations. The typical setup comprises a coherent light source, imaging optics incorporating a shearing element (such as a beam–splitter or prism), a camera sensor and digital phase‐stepping or Fourier‐based algorithms for quantitative analysis. Applications span aerospace composite inspection, pipeline weld integrity, wind‐turbine blade maintenance and civil infrastructure monitoring. Recent advances have focused on real‐time phase retrieval, deep‐learning-assisted defect classification and the extension to thick or highly scattering materials via tailored thermal or mechanical loading. The global uptake of digital shearography has grown as industries seek rapid, reliable screening tools that minimise downtime and do not require surface preparation or couplant media.

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In 2023, researchers introduced a robust phase‐extraction framework to overcome spectrum overlapping in shearographic interferograms. By combining adaptive filtering with clustering algorithms, the method separates high‐frequency fringes from speckle noise, yielding improved phase‐map quality in dynamic loading scenarios. This advance permits accurate strain measurement with fewer frames and enhances on‐site inspection speed.

A 2022 study examined defect detection in thick glass fibre‐reinforced polymer laminates under thermal loading. Finite element modelling was coupled with experimental shearography to determine thresholds for defect‐induced phase change. The work demonstrated that even at thicknesses exceeding 50 mm, subsurface flaws produce measurable deformation patterns, enabling reliable detection in marine and civil composites.

Another 2022 investigation employed spatially modulated heating for deep‐defect identification in thick composites. By replacing uniform heating with a patterned heat flux, the researchers achieved increased sensitivity to deeper flaws. Comparative tests revealed that spatial heating improved defect contrast by up to threefold relative to conventional global heating, advancing quantitative shearographic inspection.

Digital Shearography for Non-Destructive Evaluation publication trend

The graph below shows the total number of articles in digital shearography for non-destructive evaluation across all publications each year (not limited to Nature Index journals).

Technical terms

Shearography: An interferometric NDE technique that introduces a lateral displacement between two images of the same speckle pattern to measure strain gradients.

Phase Map: A two‐dimensional distribution of optical phase differences representing relative surface deformation or strain.

Spatial Phase Shifting: A method that imposes known lateral phase shifts across an image to enable quantitative phase reconstruction from a minimal number of captures.

Thermal Loading: The application of controlled heating to induce thermal‐expansion strains, enhancing subsurface defect visibility in shearographic measurements.

Finite Element Method (FEM): A numerical technique for modelling stress, strain and thermal fields in complex structures to predict deformation responses used alongside shearography for interpretation.

References

1. Digital Shearography for NDT: Phase Measurement Technique and Recent Developments. Applied Sciences (2018).
2. A robust phase extraction method for overcoming spectrum overlapping in shearography. Light Advanced Manufacturing (2023).
3. Shearography non-destructive testing of thick GFRP laminates: Numerical and experimental study on defect detection with thermal loading. Composite Structures (2022).
4. FEM-assisted shearography with spatially modulated heating for non-destructive testing of thick composites with deep defects. Composite Structures (2022).