Engine Titanium Consortium - Center for Nondestructive Evaluation ...

Project 3:
Task 3.1:
Subtask 3.1.3:
Inspection Systems Capability
Assessment and Validation
POD Methodology Applications
POD of Eddy Current
Inspections in the Field
Team Members:
HW:
GE: Dick Burkel, Jon Bartos, Shridhar
Nath, Walt Bantz
ISU: Bill Meeker, Norio Nakagawa, Bruce
Thompson
PW: Kevin Smith, Dave Raulerson, Taher
Aljundi
Students: none
Program initiation date: June 15, 1999. All effort was stopped on March 17, 2000.
Objectives:
• To develop a new methodology for estimating the POD and PFA of eddy current (ET)
inspections in the field which facilitates prediction of POD and PFA for specific changes in test
parameters, surface conditions, material noise characteristics and feature geometries in a rapid
fashion without the need to construct extensive specimen sets.
• To validate that methodology by comparing its POD results to corresponding predictions of
existing methodologies, such as the a-hat versus a model, when sufficient data exists to
support that comparison.
• To apply the methodology to the estimation of POD/PFA of inservice inspections of flat plates and
slots.
• To transfer the resulting software and procedures to the OEM’s for their use in life management
calculations.
Approach:
As in the previous work on UT, the methodology will be based on the determination of the
distributions of signal and of noise, with physical models of the measurement process being used to
allow the maximum information to be obtained from limited experimental data. Special emphasis
will be placed on the needs imposed by the development of field durability issues.
The incorporation of physical models of the inspection adds flexibility and extensibility to the
methodology, while reducing the cost. In general, physical models make parametric studies
inexpensive, by repeated computations of output signals for a wide range of inspection parameters.
The specific benefits of the models used in POD/PFA analyses are twofold:
• The model-assisted POD/PFA estimation significantly reduces the specimen preparation,
compared to a purely experiment-based POD estimate. The economic benefit is substantial for
flat-surface geometry since only a handful of crack specimens are sufficient to provide
normalization and model predictions can then cover a wide range of parameters. The benefit is
even more substantial when complex geometries are considered because, without models, one
Quarterly Report – January 1, 2002 –March 31, 2002
print date/time: 6/6/2002 - 8:39 AM – Page 106