Interferometry and Shearography:

The shearography belongs to the interferometric procedures. Interferometric measurement procedures determine the relative phase differences between (two) lightwaves, which covered different ways. In this manner, appearances which affect phases of rays of light, can be recorded by measurement technology. In the practical application these can be e.g. deformations or movements of surfaces, on which light rays are being reflected or density changes e.g. in fluids, which are being radiographed by light waves.

Interferometric setup of shearography:

Usually, the relative light phase is being determined compared to a fixed reference ray. This is comparatively sensitive compared to environmental influences, as e.g. rigid body motion. isi-sys sensors in contrast, determine the distance between two neighbour rays. In this manner, environmental influences can be compensated, as the environment influences both rays similarly. isi-sys-shearography-sensors offer for this reason a maximum in sensitivity without additional vibration isolation.

Terms of shearography / ESPI:

Is shearography not being driven via conventional film technology, but via (digital) video technology, as usual today, it can be assigned to the term electronic speckle pattern interferometry (abbr. ESPI). The addition ‘speckle pattern’ references an interferometric effect, which appears with this technology. Here it’s a matter of a visible speckle pattern, which results of superpositioning of coherent light on the image plane (eye or camera) by a diffuse reflection on a surface (e.g. of the object). The average size of the speckles is being affected by the parameters of the image (aperture and distances).

Notation:

Beside the abbreviation ESPI , the special abbreviation ESPSI is also used with the addition for the shearography (electronic speckle pattern shearing interferometry).

Shearography and non destructive testing:

An important area of application of shearography is non-destructive testing. Defects become visible on the basis of the measured inhomogeneous deformation- respectively strain distributions. Beyond the localisation, the defects or the mechanic structure of the object can be further characterised dependent of the spatial distribution. The identification of material parameters of damaged areas is possible as well in combination with fem-models. Due to high sensitivity, only little loads are required.

Methods of load for the shearographic non-destructive testing:

(Inner) pressure changes, vacuum and heat, as well as mechanic / dynamic excitation(- application) belong to the common methods of load. isi-sys has developed the dynamic excitation to the most versatile and reliable excitation method for shearographic inservice-inspections. The procedure is being applied in particular with new compound material for aerospace component (- dynamic excitation method).

Shearography NDT ESPI Vibrography method

- Overview - ESPI Vibrography method - Dynamic excitation method

- System features - Application

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