__Shearography __

hearography - Non Destructive Testing (NDT)

Shearography is an optical, Non- Destructive Testing (NDT) technique that provides fast and accurate indications 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 out-of-plane deformation. When a test object is subjected to an appropriate load, a proportional strain is induced on the test surface. If underlying discontinuities are present, the surface will deform unevenly at these locations. This is then interpreted through the shearing interferometer as a change in the phase of the laser light.

Shearograpy allows users to measure and qualify both large and small complex geometries quickly and efficiently, yielding near real-time results. Dantec Dynamics’ sheaorgraphy systems offer users the significant advantage of live phase mapping during measurement acquisition.

Before stressing, an (unloaded) reference image is taken of the material surface. All the following (loaded) states are then compared to this reference image. The yielded result is hence the difference between the unloaded and loaded material structure, where the resulting surface deformation is directly linked to the out-of-plane surface strain of the material surface.

Shearography - Non Destructive Testing (NDT) Measurement Systems

A shearographic inspection requires the stressing or excitation of a component surface. Stressing technqiues include, but are not limited to: mechanical, thermal, partial vacuum, ambient (full) vacuum, mechanical-vibration and acoustic-vibration. These excitation options show users the potential and versatility of shearography in comparison to other NDT techniques, as the combination of loading type and loading amount can be optimized for various materials.

Using the correct excitation method, the measurement images can indicate if and where any subsurface weaknesses or anomalies are present. Measurements may be evaluated in real-time or alternatively, during post-processing and recorded as individual measurement steps. Phase Stepping also allows the direction of surface movement to be interpreted, with higher and sharper defect resolution, including the advantage for users to accurately size defects.