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Shearography (alternative spellings: Scherography or English Shearography) is the abbreviation for Laser Speckle Shearing Interferometry , a coherent optical measurement method based on the laser speckle technology. If an optically rough surface is coherently illuminated, a grainy structure, which is referred to as a speckle pattern , becomes visible when it is imaged on the image plane . Shearography can be used for non-destructive material and component testing (NDT), for stress and strain measurement and for qualitative or quantitative vibration measurement under industrial conditions.

Classification of the shearographic measurement methods

Shearography inspection system

Shearography measuring method.jpg

How digital shearography works

The illustration below shows the structure and functionality of simple digital shearography. The measurement object is illuminated with an expanded laser beam . The surface of the measuring object reflects the laser beam, which falls on the image plane of a digital camera . The shear element creates two slightly shifted images of the object in the image plane, creating an interferogram .

If one now correlates two interferograms recorded in different load states of the measurement object, a characteristic stripe image is created, which is referred to as a sherogram. In the simplest case, the correlation consists of a point-by-point subtraction of the gray values ​​of the individual images and subsequent formation of the absolute value. The analysis of the shearogram allows conclusions to be drawn about material inhomogeneities under the component surface, since material defects lead to inhomogeneous surface deformation.

The stripes in the shearogram can be interpreted as contour lines of the deformation gradient. This distinguishes shearography from holographic interferometry (HI) and from electronic speckle pattern interferometry (ESPI). In the HI and ESPI methods, the interference pattern represents the deformation itself. The holographic interferometry is explained in the article holography , ESPI is described in Electronic Speckle Pattern Interferometry .

In contrast to HI and other interferometric techniques, shearography is relatively insensitive to vibrations, as both interfering partial waves are guided over the measurement object. Changes in the optical paths due to vibrations therefore largely compensate each other. This is why shearography is also used in "rough" environments.

The wedge angle of the shear element determines the size of the shear. An optical wedge or a biprism can be used as the shear element. Alternatively, an optical structure based on a Michelson interferometer can also be used. In this case, the shear is achieved by tilting an interferometer mirror slightly. This has the advantage that the size of the shear can be adjusted continuously.


Schematic structure of the simple digital shearography

Applications in industry

Shearography is used in compact devices for mobile inspection with combined temperature and / or vacuum loads in industry, especially in aviation for the non-destructive testing of composite components. The focus here is primarily on the time-saving and user-friendly testing of changing or the same tasks.


The German Institute for Standardization (DIN) has had a corresponding DIN standard for shearography since 1997 . The ASTM International has addressed this issue already in a standard.

  • DIN 54180-1: 2015-01 Non-destructive testing - Shearography - Part 1: General principles
  • DIN 54180-2: 2016-12 Non-destructive testing - Shearography - Part 2: Devices
  • DIN V 54180-3: 1997-03 Non-destructive testing - Shearography - Part 3: Testing of pipelines (currently withdrawn)
  • ASTM E2581-07 Standard Practice for Shearography of Polymer Matrix Composites, Sandwich Core Materials and Filament-Wound Pressure Vessels in Aerospace Applications

DIN V 54180-3 is still a pre-standard .


  • Thomas Kreis: Holographic Interferometry. Principles and Methods. Akademie-Verlag, Berlin 1996, ISBN 3-05-501644-0 ( Akademie Verlag Series in Optical Metrology 1).
  • PK Rastogi (Ed.): Holographic Interferometry. Springer, Berlin et al. 1994, ISBN 3-540-57354-2 ( Springer Series in Optical Sciences 68).
  • Wolfgang Steinchen, Lianxiang Yang: Digital shearography. Theory and application of digital speckle pattern shearing interferometry. SPIE Press, Bellingham WA 2003, ISBN 0-8194-4110-4 .
  • U. Schnars, C. Falldorf, J. Watson, W. Jüptner: Digital Holography and Wavefront Sensing (Second Edition) . Springer 2014, ISBN 978-3-662-44692-8 .

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