Embedded Digital Speckle Pattern Interferometry for Three-dimensional Strain Analysis

Abstract

The extension of Digital Speckle Pattern Interferometry to three-dimensional cases poses new challenges from both the practical and the theoretical points of view. In the present research, a scattering surface was created within a transparent Plexiglas specimen with the aid of atomized aluminum particles, and strain was measured in the interior plane. Test specimen configurations included a beam in bending and a disc in diametral compression. The tests on the beam in bending showed excellent agreement between Embedded DSPI results and resistance strain gages. However, for the disc in compression, large discrepancies were found. The main source of errors was identified in the effect of the refractive index gradient. Based on the assumption that the index of refraction changes proportionally to the local dilatation, the error was calculated and the predicted results were ultimately in good agreement with the DSPI data. In conclusion, the Embedded DSPI technique was found to be a viable tool for direct experimental strain investigation of complex 3-D cases.

Comparison of the Mechanical Behaviour of Standard and Auxetic Foams by X‐ray Computed Tomography and Digital Volume Correlation

“…However, these methods are often too sensitive for a lot of applications and are hard to set‐up and expensive, even though they provide excellent quality data, as seen in , for instance. Similar ideas using interferometry but with optical ‘slicing’ have been experimented in . It should be noted that such techniques can be spoilt by the presence of strain‐induced light index variations (photo‐elastic effect), which can however be accounted for .…”

“…Similar ideas using interferometry but with optical ‘slicing’ have been experimented in . It should be noted that such techniques can be spoilt by the presence of strain‐induced light index variations (photo‐elastic effect), which can however be accounted for . Finally, neutron and synchrotron X‐ray diffraction have also been widely used to map in the elastic strains at specific points, along specific lines or across 2D sections , but only elastic strains are measurable and for certain materials only.…”

Light-scattering measurements of micro-deformations in granular materials

“…Contrary to most actual speckle methods which are based on surface reflection, in our case rays propagate inside the sample. More precisely in the backscattering configuration the optical rays probe a volume of typical size (l * ) 3 in the vicinity of the illuminated surface, as shown schematically on Figure 1(a).…”

“…Such optical methods provide a map of the deformation at the surface of a sample or in a plane embedded in a transparent sample [3]. We propose a new full-field optical method based on Diffusive Wave Spectroscopy [4,5].…”

Diffusing‐Wave Spectroscopy Contribution to Strain Analysis

“…The use of digital image correlation and interferometric techniques (speckle or holographic interferometry) has spread [1, 2]. These optical methods are non‐intrusive and provide a map of the deformation at the surface of a sample or in a plane embedded in a transparent sample [3]. All those methods are based on the fact that the light is scattered by the surface of the sample, that is, the incident ray and the reflected ray intersect at a given point of the surface.…”