Engine Titanium Consortium - Center for Nondestructive Evaluation ...

• To use this methodology to assess the improvements in POD afforded by the Production
Inspection Task 1.3.2.
Approach:
This task will extend and apply the approach used in Phase I for billets to develop a method for
estimating POD of naturally occurring flaws in forgings. The methodology developed in Phase I is
based on detection theory concepts involving distributions of noise and of flaw response in the
presence of noise. In this subtask, that methodology will be applied to the case of forgings, with a
major extension being related to predicting the POD as a function of position within the forging.
The proposed program consists of four major elements, which have been selected in response to
the issues identified above.
Application of the Methodology to Sonic-Shaped Forgings: Initial work in Phase II will use designed
experiments to specify distributions of noise and signal response in existing blocks of forged
material containing FBHs and/or SHAs. The initial focus will be on the effect of material anisotropy
that results from flow lines created by the forging process on POD. The first step will be
determination of the magnitude of anisotropy, which will be determined in subtask 1.3.1,
Fundamental Studies. Given that information, the flaw response and noise models will be modified
to take into account this anisotropy. Appropriate statistical distributions will then be developed,
based on a combination of these models and experimental data to describe the distributions of
signal and noise response for a simple forging geometry. Any further modifications to the
methodology needed to take into account anisotropy will be made.
When samples become available from Task 1.3.2, similar, but more extensive, experimental studies
will be conducted on sonic-shaped forgings. These experiments will be conducted with samples
containing flat bottom holes placed at some number n (to be determined later) positions in the
sample. The positions will be chosen to provide a range of inspection geometries, surface
curvatures, flaw depths, etc. Because of the symmetry of sonic-shaped samples, it will be possible
to replicate these synthetic flaws systematically around the sample unit to allow a study of the
variability of the responses of nominally identical flaws (providing important information needed to
quantify sources of variability in signal response). Initial scanning, analysis, and modeling will be
done on a representative sample of n/2 of the seeded flaw positions. The experimental data will be
important for developing a methodology that will account for the strong effect that flaw location will
have on POD with complicated geometries. The data will be analyzed to check and tune the
deterministic signal-response model and to develop appropriate statistical models for the variability
in the signal response measurements, the important components of the POD prediction model.
The resulting POD prediction methodology will then be used to predict POD at the other n/2
positions, to validate the results. The data generated during these scans will also be used to
provide a database which will be used in the development of noise distributions, as influenced by
surface curvature.
Because a significant amount of the data will be generated in the above study, it should be possible
to compare POD predictions from the new methodology with predictions of existing methods such
as the ahat vs. a and the R e methods. Such comparisons will be made to provide an important
check on the different aspects of the methodology over the required wide range of inspection
conditions encountered in forgings. Efforts will be initiated to take into account the morphology of
Quarterly Report – January 1, 2002 –March 31, 2002
print date/time: 6/6/2002 - 8:39 AM – Page 99