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Foundation ::
CAD CAM CAE ::
SDVIC
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SDVIC
Sub-Pixel Digital Video Image Correlation
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SOURCE CODE AVAILABLE
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Sub-pixel Digital Video Image Correlation (SDVIC) is a technique to measure in-plane displacements on the surface of objects under loading, without contact. This
system can be used for analyses of experimental research specimens or actual service structures of virtually any size or material. Test objects require minimal preparation
and need not be isolated from vibration or temperature fluctuations. The SDVIC software produces color-graduated, full-field representations of in-plane displacements
and their partial derivatives with respect to both directions. From this, linear strains, shear strains, and rotation fields may be determined.
SDVIC is based upon a computer algorithm to locate small regions of a random pattern after the pattern has been deformed. The SDVIC software determines values for
in-plane displacements and strains by correlating the positions of pixel subsets in the original image to those in the deformed image based upon pixel gray levels in the
digitized images. The size of subsets to be pattern matched may be customized, thus allowing many random patterns to be correlated. Several techniques, including a
coarse-fine search and the Newton-Raphson method, are available for subset pattern matching. A bilinear interpolation routine provides sub-pixel resolution necessary
for most displacement and strain measurements.
To utilize SDVIC, one needs a black and white video camera to acquire images of the test article before and after loading. Camera lens combinations may be altered to
allow analyses of virtually any size of test article. A PC based video board is typically used to digitize these images. These images are then correlated by a PC equipped
with the SDVIC software. All of the components required for a typical system are commercially available. There is no need for custom equipment which is expensive or
difficult to find.
In order to properly correlate images based upon subset gray level patterns, the test article must have a characteristic pattern on its surface. This pattern may be naturally
occurring, such as the grains and grain boundaries of metals under microscopic magnification, or the pattern may be applied by dusting the specimen with fine particles
or over-spraying the specimen with white and black spray paint. Pattern application typically requires only a few minutes and a few dollars for several specimens.
SDVIC carries the NASA case number MFS-26289. It was originally released as part of the COSMIC collection.
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More software from National Technology Transfer Center
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