Nondestructive Inspection (NDI) of Fastener Holes in Thick Multi-Layer Structure

Innovative Materials Technologies, Inc. (IMTT) teaming Boeing West is proposing Flat Geometry Remote Field & Super Sensitive Eddy Current (FG RFEC & SSEC ) technique for inspection of fastener holes in thick multi-layer structures. To detect cracks in a multi-layer Ti-Al-Ti ¡VAl structure with two thicknesses, 0.38¡"+2.0"+0.38"+0.65¡" and 0.9¡"+0.9¡"+0.9¡"+0.5¡", as described in the Topic AF04-134, is a big challenge to any exiting or emerging NDI techniques. Examples include: 1. Ultrasonic techniques (UT), including guided UT, are incapable of penetrating through air gaps between two adjacent layers without sealant. 2. Most eddy current techniques (ECT), including these emerging techniques, such as MOI, MWM, EC array, Rivet Check, etc., have inherently limitation in penetration depth from their working principle ¡V the Skin Depth. They have little potential in further extending their penetration depths. 3. Super-conductive Quanta Interface Device (SQUID) can have deeper penetration with the help of super conducting materials working at extremely low temperature. However, the cooling system and the low temperature itself create problems, such as large size and weight, high cost, high noise, etc., which are not acceptable in practical aircraft NDI applications. Among all ECT¡¦s the FG RFEC & SSEC is the only one that its penetration depth is not limited by Skin-Depth, because the signal received by its receiving unit has penetrated through the object wall twice and carries clean signal about the wall conditions. Therefore, FG RFEC & SSEC is the most promising technique in reaching the goal set in this project topic description. Current FG RFEC & SSEC technique uses only about 0.4 watt for driving a probe and is capable of detecting flaws that are 0.8¡" below surface in multi-layer aluminum structures. There is not any question to increase the driving power to 10 or even 100 times and further extend its penetration depth many times. Replacing the currently used coil sensor with a magnetic sensor, such as GMR, would make more increase in the sensitivity of the FG RFEC & SSEC technique. In this project IMTT will be responsible for the development of the proposed technique, while Boeing West will provide guidance, the NDI experiences working with B1-B airplane, tests specimens and validation of the technology development. The Phase I objective is to prove the potential and feasibility of the proposed technique in detecting cracks deeply hidden in thick and multi-layer structures described in Topic Description. Two approaches, numerical simulation and experimental test, will be conducted in parallel. By the end of Phase I a presentation/demonstration will be performed to show the simulation and experimental test results on specimens provided by AFRL/Project Sponsor. Mr. Sun, Yushi, President of IMTT and Principal Investigator, has more than 18 years experiences in R&D of FG RFEC & SSEC technique, as well as in finite element modeling of electromagnetic NDI phenomena. He is an active and Founder Member of International Computation Electromagnetics Society, COMPUMAG and was a Session Chair and a member of the Editorial Board for a number of international conferences in computational electromagnetics and electromagnetic NDI. Dr. Masood A. Zaidi from NDE Materials and Processing Technology, Boeing West at Long Beach, CA, will be the Co-Principal Investigator.