Experimental comparison between a portable DSPI device with diffractive optical element and a hole drilling strain gage combined system

This paper presents a portable device to measure residual stress fields outside the optical bench. This system combines the hole drilling technique with digital speckle pattern interferometry. The novel feature of this device is the application of a binary diffractive optical element (DOE) in order to generate double illumination and radial in-plane sensitivity. The use of the DOE ensures constant sensitivity since it only depends on the grating period, having lack of dependence on the wavelength of the illumination source. Descriptions of the DOE and the portable device are followed by the presentation of experimental results showing that the combined system can measure residual stress fields with an uncertainty of 7%. On the other hand, these fields were measured with the traditional strain gage hole drilling technique. A set of results obtained for a residual stress level of 45% of the yield stress of the material, showed a good agreement between both evaluated systems.