Laser Shearography is a very sensitive, non contact, non invasive Non Destructive Testing method that is able to visualize the strength of a component under test.
The system uses a CCD camera with a shearing lens to view laser light reflected from the surface under inspection. , The effect of the overlapping sheared images is to bring two separate points on the object surface to meet in the image plane. The two overlapped portions of the sheared images interfere and produce a speckle pattern. When an applied stress deforms the specimen, the speckle pattern is slightly modified. Comparing the two speckle patterns (stressed and unstressed) produces a fringe pattern which depicts the relative displacement of the two neighbouring points.
Since the magnitude of image shearing is small, the fringe patterns approximately represents the derivative of displacement (strain) with respect to the shearing direction. This differs from holography which depicts displacement rather than its derivative.
State of the art computing enables Phase Stepping shearography that has increased the sensitivity of the inspection dramatically and allows engineers greater flexibility in defect detection. Dantec Equipment has the ability to couple with whole field imaging, 3-Dimensional analysis, out-of-plane 1st differential of displacement profiling, and image integration.

Laser Shearography is an ' Active’ NDT process which requires the material under examination to be stressed to reveal the defects. The stressing can take many forms, the optimum being the one which differentiates defects from the parent material, with the ability to find the minimum defect standard. Thermal, ambient pressure reduction (applied to the surface or in a chamber), pressurisation, vibration (direct mechanically coupled or remotely acoustically coupled), or even hand pressure. Is used to find the defects

Laser Shearography utilizes the relationship between stress, strain and material strength. The basic fringes of a shearography result are lines of iso-strain, therefore the application of stress to a part resulting in lines of iso-strain give an indication to the material strength. It therefore implies that a uniform material should deform uniformly under uniform load. Variations in the strain field depict variations in material strength. The greater the fringe density the weaker the material.

Laser Shearography views only the surface and does not penetrate into the material. A subsurface defect, disbond or feature will affect the surface strain field and is detectable. The principle sensitivity is in the out-of-plane direction, but there is a small in-plane component, this combination fully interrogates the material under test