Interior strain fields in polymethylmethacrylate thick specimens are measured by an embedded digital speckle pattern interferometry (DSPI) method. The specimens contain an embedded reflecting-scattering surface in an interior plane. This is obtained by bonding two parts of the specimen with cyanoacrylate mixed with atomized aluminum powder. Specimens are beam-shaped and loaded in both four-point and three-point bending. The interferometer is in-plane sensitive and the phase difference maps are calculated using a four-step phase- shifting algorithm. The displacement maps are unwrapped and then, using least- square polynomial fitting, interpolated and differentiated to obtain strain. DSPI data is acquired for surface strain and strain within the material through the thickness. Comparisons using electrical resistance strain gages (RSGs) mounted on the specimens are performed for validation. Results obtained with 'embedded' DSPI agree with RSGs, with errors averaging around 10%. Possible sources of errors have been analyzed. The method appears to be competitive with other techniques available in literature.
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