Phasemaps obtained by phase shifting techniques in digital photoelasticity contain ambiguous zones. To obtain total fringe order by phase unwrapping, the phasemap should be free of ambiguous zones. A new method is developed, which uses a dark field image for ambiguous zone identification and its correction. This methodology is explained and validated by solving a benchmark problem. As ambiguous zones are of arbitrary shape, an advanced boundary extraction method developed in-house is used for effecting the correction in practical problems. The performance of the new methodology is demonstrated by using the problem of a ring under diametral compression and a slice cut from a stress frozen model.
Recently, stereolithography, one of the rapid prototyping (RP) techniques, has simplified the process of making three‐dimensional (3‐D) photoelastic models. One of the issues in stereolithography‐made models is the noise due to porosity of the model. This is undesirable for data handling in digital photoelasticity. A preliminary study showed that the thickness of the slice has an influence on the appearance on the noise. In this paper, use of 10‐step phase‐shifting technique (PST) and refined three‐fringe photoelasticity (RTFP) is explored to determine the isochromatic data as accurately as possible. A slice cut from a 3‐D model of a spline shaft made of stereolithographic material is used for isochromatic determination. It is found that with suitable postprocessing, the quantitative results obtained from 10‐step PST and RTFP are comparable. The relative merits of these two techniques for analysing stereolithographic models are brought out.
Digital photoelasticity is an experimental method for determining stresses in 2D and 3D
models. In digital photoelasticity one gets a wrapped isoclinic phasemap. The main issue with
wrapped isoclinic phasemaps is that the isoclinic values obtained do not uniformly represent the
principal stress direction of one of the principal stresses consistently over the entire domain. These
zones are labelled as inconsistent zones. Such zones need to be identified and corrected to get
unwrapped values of continuous isoclinic phase values. In this paper, a method is developed to plot
the simulated wrapped and unwrapped isoclinic phasemap from 2D Finite Element (FE) results so
that one can use this as a convenient tool for identification and correction of inconsistent zones in
isoclinic phasemaps obtained experimentally for complex problems. The method is explained by
using the problem of a circular disc under diametral compression. The application of this method
for handling complex problems is demonstrated by solving the cantilever bending of a binocular
specimen.
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