Engine Titanium Consortium - Center for Nondestructive Evaluation ...

must prepare a large number of specimens of varying defect sizes and conditions to perform
POD analyses for each new inspection geometry. The expense of this approach often leads to
a best effort approach rather than a rigorous statistical study of the required number of
samples.
• Models make POD/PFA results transferable. For instance, suppose that the distributions have
been determined for a given probe and the POD/PFA estimated. The model can then be used
to transfer this POD/PFA result to another probe, with appropriate correction factors, because
of the model’s ability to reliably predict relative signal strengths between one probe and
another. Also, the model allows results to be transferred from one geometry [e.g., straight
edges] to another geometry [e.g., slot edges]. Collectively, the use of models can reduce the
cost and time requirements of POD/PFA analyses to more manageable levels in an
environment where both inspection demands and opportunities are increasing. This results not
only in cost savings, but more importantly, increases the likelihood that formal POD/PFA
estimates will be made with enhancement to safety and quantification of the benefits now
possible.
Figures 4 and 5 present flow diagrams of the work plan that has been developed to accomplish
these goals, as is discussed in detail in the following text.
a
Notch
& crack
specimens
h
ET measurement
b
1D line/
2D raster
scan data
g
Physical probe
response
model
(flaw & geometry)
c
Data
analysis
Validation
Noise
component
Flaw
signal
Geometry
signal
d
e
Monte Carlo
(Scan index,etc)
f
i
Stat. model of
noise
distribution
j
Stat. model of
signal
distribution
l
Crack
morphology
database
k
POD, PFA,
ROC
Figure 4. Detailed experimental and validation plan for EC methodology.
Quarterly Report – January 1, 2002 –March 31, 2002
print date/time: 6/6/2002 - 8:39 AM – Page 107