Non-deterministic Calibration
169
Fig. 1 Digital image correlation example
measured local data set would be displacements or strain obtained through the use
of DIC, which is explained in Sect. 2.2.1. The full-field data could also be used
to produce global data by extracting displacements or strains from virtual strain
gauges, which extract averaged values over their length during post-processing of
the DIC data. In the context of deformation of polycrystalline materials, local DIC
data can be used to quantify deformations within each grain in the polycrystalline
aggregate. This approach requires that the underlying microstructural features be
aligned with the DIC data. The underlying microstructure morphology can be measured using electron backscatter diffraction (EBSD), which provides quantification
of the surface grain shapes and their orientations. Additionally, high-resolution
EBSD (HREBSD) can be used to compute the elastic deformation gradient locally
on the surface of a specimen. An overview of EBSD and HREBSD is provided in
Sect. 2.2.2.
2.2.1 Digital Image Correlation
DIC is a metrological tool used for quantifying motion/deformation that occurs
between a reference image f (x, y) and a deformed image g(x , y ) (see Fig. 1).
By maximizing the correlation of features within f and g, a mapping can be
found between (x, y) and (x y ). Ultimately, that mapping comes in the form
of a displacement field (usually a spatial array of displacements) [28, 40]. The
displacements can be further processed to give estimates of local strains. A
limitation in the above-described two-dimensional DIC is that displacements can
only be measured in the plane of the image, i.e., displacements and strains with
components in the Z-direction are not identified. Stereo-DIC is able to identify outof-plane motion with the use of a two-camera setup. However, because images can
only be taken of the surface of a specimen, strains with respect to the throughthickness dimension, i.e., into the specimen, are still not identified.
169
Fig. 1 Digital image correlation example
measured local data set would be displacements or strain obtained through the use
of DIC, which is explained in Sect. 2.2.1. The full-field data could also be used
to produce global data by extracting displacements or strains from virtual strain
gauges, which extract averaged values over their length during post-processing of
the DIC data. In the context of deformation of polycrystalline materials, local DIC
data can be used to quantify deformations within each grain in the polycrystalline
aggregate. This approach requires that the underlying microstructural features be
aligned with the DIC data. The underlying microstructure morphology can be measured using electron backscatter diffraction (EBSD), which provides quantification
of the surface grain shapes and their orientations. Additionally, high-resolution
EBSD (HREBSD) can be used to compute the elastic deformation gradient locally
on the surface of a specimen. An overview of EBSD and HREBSD is provided in
Sect. 2.2.2.
2.2.1 Digital Image Correlation
DIC is a metrological tool used for quantifying motion/deformation that occurs
between a reference image f (x, y) and a deformed image g(x , y ) (see Fig. 1).
By maximizing the correlation of features within f and g, a mapping can be
found between (x, y) and (x y ). Ultimately, that mapping comes in the form
of a displacement field (usually a spatial array of displacements) [28, 40]. The
displacements can be further processed to give estimates of local strains. A
limitation in the above-described two-dimensional DIC is that displacements can
only be measured in the plane of the image, i.e., displacements and strains with
components in the Z-direction are not identified. Stereo-DIC is able to identify outof-plane motion with the use of a two-camera setup. However, because images can
only be taken of the surface of a specimen, strains with respect to the throughthickness dimension, i.e., into the specimen, are still not identified.