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Laser shearography

Laser shearography is derived from holography and is an optical technique that provides fast and accurate information about internal material discontinuities or anomalies in non-homogenous materials. Using laser light, a shearing interferometer is able to detect extremely small (sub-micrometer) changes in surface deformation. When a test object is subjected to an appropriate change in load, a proportional strain is induced on the test surface. If underlying surface discontinuities are present, the surface will deform unevenly which is interpreted through the interferometer as a shearographic image. Shearograpy allows users to measure and qualify large surfaces quickly and efficiently, yielding near real-time results.

An initial image (known as a shearogram is taken with the structure unloaded in order to create a reference image. Then incremental load is applied, causing deformation of the surface being tested. Further shearograms are recorded as load is increased. Subtraction of initial and subsequent images yields visible interference patterns that are related to surface strains.

Suitable materials and applications for use of laser shearography include carbon fibre spars and fittings (for which the technique is valuable in looking at cracks, delaminations and stress build up at possible failure points such as the attachment points of fittings) and composite and sandwich structures such as hulls, decks and superstructures (for which the technique is valuable in looking at cracks, delaminations, bonding failure and stress build up around fittings, hard points and reinforcement).

To discuss how laser shearography might be of use to you, please get in touch using our Contact Us page or via the link opposite.

 

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