Simultaneous out-of-plane and in-plane displacements measurement by using digital holography around a hole or indentation

A measurement prototype based on digital holography for the simultaneous measurement of out-of-plane and radial in-plane displacement fields is shown. This prototype enables recording two holograms at the same time with a single image taken by a digital camera and evaluating separately in-plane and out-of-plane displacement components. An axicon-type diffractive optical element (DOE) is used for the illumination of the object, which causes radial sensitivity vectors. Blind holes as well as spherical indentations were preformed over a welded steel plate (containing residual stresses). By using the digital holography setup, typical out-of-plane and in-plane displacement fields, generated when the hole was introduced into the stresses material, were measured and compared with theoretical ones. Good agreement was found between them. In addition, a mature digital speckle pattern interferometry (DSPI) setup was used to measure only the in-plane component around the hole. Good agreement between both systems was also found. Finally, displacements fields were measured around indentation marks. In this case, preliminary results show that out-of-plane displacements are larger than in-plane ones, enabling its use for residual stress computation or maybe material properties determination.