Computational Methods for Debonding in Composites

9 Progressive Damage Modeling of Composite Materials 187
a 4 point bend test) and absorbed energy during the damage process are consistent
with the measured quantities from the OCT test.
Recently, an advanced image processing technique has been used to extract the
crack length and damage height information from the OCT tests in a more accurate
and less invasive manner. In this method, the specimen is treated with a speckle
pattern and several images of the specimen are recorded during the test using a
camera. These images are then processed by a computer software which produces
the displacement and strain fields as output. This method enables the quantification
of the local displacement/strain fields in the critical positions such as the damage
zone. Figure 9.5 shows an example of the strain field contours that can be extracted
from an OCT test using the image analysis software [12].
Figure 9.6 shows the strain profiles at a section close to the notch tip and perpendicular
to the crack line. The strain profiles for two different levels of pin opening
y
x
Fig. 9.5 An example of the strain field calculated by the image processing software, DaVis [12].
The arrow shows the position of the initial notch in the OCT test [15]
POD = 3.17 mm
POD = 2.86 mm
h c = 20.8 mm
0.3
0.2
0.1
0.0
h c ~ 18 mm
Fig. 9.6 Longitudinal strain profiles at two different levels of pin opening displacement (POD)
along a vertical line through the damage zone in an OCT test specimen using the image analysis
software, DaVis [12]