Combined speckle interferometry and speckle correlation for non-destructive testing

Sammanfattning: When a sample is studied during loading in a tensile test machine, the sample is often exposed to rigid body motions during loading at the same time as it deforms due to tension. Therefore, the small deformation field is hard, or impossible, to measure when it is overlaid by a large motion. The large rigid body motions can be measured with methods like speckle correlation (also called digital speckle photography, DSP), but the results might be of too poor accuracy to resolve the deformation field. Interferometric methods on the other hand might measure the deformation field but the rigid body motion makes the fringes disappear. In this thesis a method is presented that makes it possible to master such measuring situations, by a combination of speckle correlation and speckle interferometry (also called TV holography, ESPI or DSPI). Both theory and experiments are presented. It is shown that speckle correlation can determine the speckle motion in the recording in order to determine the small deformation field in the interferometric algorithm. Speckle correlation can also be used to determine the amount of shear in shearography allowing a quantitative determination of the spatial derivative of the deformation field.