| סיכום: | Strain and deformation measurements are common properties measured using traditional
equipment, such as extensometer. But, it has limited measuring range. Because of that, the idea
of using digital image correlation has been raised. However, the accuracy of this method for
practical application is not well researched. This project aims to study this method thoroughly
with StrainMaster software to calculate strain and deformation.
Specimens were molded into cylindrical and rectangular shape. They are made from molded
Hydrocal B-11 gypsum. The prepared specimens were then painted with white color. Both
shape of the specimens were then treated with different speckle patterns and different
measurements. All of the specimens were tested with unconfined compression test.
The measurement results on cylindrical specimens with a constant step size showed that the
larger subset sizes were better at measuring circumferential strains than the smaller subset sizes
were. But, the accuracy of larger subset sizes might be affected by the average deformations
calculated inside their subsets. On the measurements using a constant subset size, the largest
two step sizes were more accurate in measuring specimens with a lot of deformation activities.
On the other hand, the smallest two step sizes were more accurate in measuring specimens with
little deformation activities. It was also found out that if the specimen has constant deformation
rate, measurements with different step sizes produced little differences. Finally, there was no
link found on the effect of density of the speckles on the accuracy of the test.
The test results on rectangular specimens showed that speckle characteristics do show effect on
the consistency of the results obtained using different subsets and calculation modes. Using fast
mode, the effect was more pronounced on anisotropic specimens than it did on isotropic
specimens. The test also found out that different mode can produced different results on the
same specimens with different contrasts.
This project showed that digital image correlation technique should be used with prior
knowledge of deformation trend and brittleness of a specimen. The choice of calculation mode
depends on the tradeoff between time and accuracy. Finally, isotropic and non-repetitive
speckle pattern is a better choice than anisotropic patterns.
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