A new hybrid method combining moire interferometry, high resolution
data-reduction technique, two-dimensional datasmoothing
method, and Finite Element Method (FEM) has been
successfully developed. This hybrid method has been applied to
residual strain analyses of composite panels, strain concentrations
around optical fibers embedded in composites, and cruciform
composite shear test.
This hybrid method allows moire data to be collected with
higher precision and accuracy by digitizing overexposed moire
patterns (U & V fields) with appropriate carrier fringes. The
resolution of the data is ± 20 nm. The data extracted from the
moire patterns are interfaced to an FEM package through an
automatic mesh generator. This mesh generator produces a nonuniform
FEM mesh by connecting the digitized data points into
triangles. The mesh, which uses digitized displacement data as
boundary conditions, is then fed to and processed by a commercial
FEM package.
Due to the natural scatter of the displacement data digitized
from moire patterns, the accuracy of strain values is significantly
affected. A modified finite-element model with linear spring
elements is introduced so data-smoothing can be done easily in two dimensional
space. The results of the data smoothing are controlled
by limiting the stretch of those springs to be less than the
resolution of the experimental method.
With the full-field hybrid method, the strain contours from
moire interferometry can be easily obtained with good accuracy. If
the properties of the material are known, the stress patterns can
also be obtained. In addition, this method can be used to analyze any
two-dimensional displacement data, including the grid method and
holography.
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