06-Defects.pdf

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D
.
EFECT
.
ANALYSIS
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he defect analysis tool offered with
VGStudio
MAX 2.1
is designed to
process voxel datasets for internal defects (voids or inclusions).
After a surface determination the tool will automatically detect
defects and provide detailed analysis results.
T
Shor tcuts
The shortcut icons for the
Defect Analysis
tool are located in the icon bar as
indicated in the image below:
launches the
Defect Analysis
tool.
creates a new defect analysis annotation.
Example
As an example of the usage of the defect detection tool an analysis will be
made on our test sample. To start please open the file called
06-Defect-
start.vgl.
From the slice images you will already notice that the part has a
fair number of internal defects showing up as darker areas within the CT
dataset:
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DEFECT ANALYSIS
In the image above the outline of the determined surface was turned off.
Original display mode
button at the bot-
This can be done by toggling the
tom of the slice view.
To start the defect analysis select the
New defect detection
icon from the icon
bar. This will launch the interface for the defect detection tool.
From a visual inspection of the CT slices a
Default
algorithm based on the
calibration
values for material and background was chosen: Choose the
Default
algorithm and click
Use calibration
. Since some of the darker areas
within the material looked relatively large the maximum defect size was set
to 100 mm³ and the minimum to 8 voxels to stay above the noise level of
the data. However since the data looked relatively free of CT artifacts all
the ignore artifacts tabs were switched off. The
probability threshold
was
reduced to 0.5 to include more possible defect candidates in the final analy-
sis result. The number of defects can later be reduced by sorting the defects
according to probability. Then by inspection a reasonable probability
threshold can be determined and all defects below the given probability
level are deleted from the list.
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DEFECT ANALYSIS
Check the
Defect size color coding
switch. This will color the detected
defects according to their volume. To start the defect analysis press the
Cal-
culate
button at the bottom of the
Defect detection
tool interface.
Once the calculation has finished you will be presented with a list of the
detected defects:
This includes information such as probability, volume, position and size of
each of the defects. Since the probability threshold was set fairly low some
of the detected defects may actually be noise within the dataset. Thus the
next step is to determine a minimal probability threshold at which a
detected defect is clearly distinguishable as such. First sort the defect list
by probability by pressing the
Probability
tab in the table. Each individual
defect can be inspected by selecting it from the list. Once a defect is
selected the slice views will be updated to show the actual defect within the
part:
Toggle the
Original display mode
to show what the detected defect looks
like in the original dataset. Keep going through the list until a probability
value is reached for which the detected defect is clearly above the level of
the noise in the dataset. In this particular case a probability level of around
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DEFECT ANALYSIS
3 seems appropriate. To delete all defects with lower probability from the
list first select a defect with a probability just below the determined thresh-
old. Scroll back to the lowest probability defect and select it from the list
while holding the
<Shift>
key to include all defects between the two. The
selected list of defects with a probability below the determined threshold
can now be deleted by pressing the right mouse button and selecting
Remove entries from list
.
Sorting the list of defects by their size you will notice that the largest
detected defect (just below 60 mm³) is well below the 100 mm³ that was set
as the initial limit. To rescale the color table accordingly select the
Colors
tab in the
Defect detection
tool. By pressing the mouse button over the
from
and
to
fields new values can be typed in. Select the
to
field and change the
value to
60
instead of
100
to scale the color table to a more suitable range.
To see the result of the defect detection in the 3D window, the surface of
the part has to be turned transparent. First select the
Volume
object in the
Scene Tree
. Then in the
Volume Rendering tool
choose the
Transparency
tab
from the
Appearance area
and reduce the value to make the volume trans-
parent and reveal the internal defects:
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DEFECT ANALYSIS
Annotations
Annotations can be created by selecting one or more defects from the
defect list and then choosing
Create annotations
from the right mouse button
menu. This will create an annotation attached to the defect in both the slice
views as well as the 3D view. The annotation includes information about
the defect size and position:
An annotation can also be created by choosing the
New Annotation
icon from
the icon bar and then pressing <Ctrl> and the left mouse button over the
defect in any of the slice views. The annotation leaf can be repositioned by
pressing and holding the left mouse button over the leaf after which it can
be dragged into a new position. The defect referenced by an annotation can
be changed in a similar fashion by moving the annotation pointer instead -
use <Ctrl> and the left mouse button to do so.
A list of the annotations and their associated properties is available via the
Annotations
tab in the
Defect detection
tool:
Defect detect ion and ROIs
It is possible to perform a defect detection limited to a specific region of a
CT dataset. This can be done by first defining a ROI (see chapter 9 - Seg-
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