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Hole Drilling Method ( 13:12 18.03.2011)

The hole drilling method is a mechanical method for measuring residual stresses and it is standardized in the ASTM E837. The basic hole drilling procedure involves drilling of a small hole diameter d0 into the surface of a stressed material. The stress equilibrium is locally disturbed due to this intervention whereby a new aquilibrium is reached. This change is measured usually radial to the hole with special stain-gage rosets in the form of relieved strains.

(Enrique Garcia Sobolevski, Residual stress analysis of components with real geometries using the incremental hole-drilling technique and a differential evaluation method, page 18)

Ring Core method (time 13:21 18.03.2011)

The ring core method is also based on the strain caused by disturbing the stress field, but in this case a relatively stress-free island of material is isolated by making a shallow ring around a strain-gage. This method is one of the least destructive mechanical stress-relief techniques and are relatively simple and economical.

(George E. Tottem, Handbook of residual stress and deformation of steel, page 110)

ESPI Electronic Speckle Pattern Interferometry (14:36 18.03.2011)

An extended laser beam is used to provide coherent illumination of a test sample which is viewed with a CCD camera or other electronic image sensor. Coherent light scattered from an optically rough test surface impresser a laser speckle pattern on the image of the test object, and the spatial characteristics of the speckle pattern are determined primarily by the finite resolution of the imaging lens. The interferometer optics, might be one of many configurations depending on the measurement objectives. The basic function of interferometer is to deliver two dinstint coherent wavefronts to the imaging system.

(Donald O. Thompson,Dale E. Chimenti, Review of progress in quantitative nondestructive evaluation, page 373)

Contour Method (15:02 18.03.2011)

In the approach of Contour method, the analysed specimen is carefully cut in two along a plane using a wire EDM machine. Residual stresses relax as free surface is created by the cut. After cutting , the contours of the two opposing surfaces created by the cut are measured using a CMM machine or by laser scanning. Assuming that the contours are caused by elastic relaxation of the residual stresses, a straightforward finite element calculation, in which the opposite averaged contour is applied as boundary conditions to the FE model, permits to reveal the original residual stresses component (sigma x) normal to the cut surface.

(E. E. Gdoutos, Experimental Analysis of Nano and Engineering Materials and Structures, page 635)