NASA 1998 SBIR Phase I


PROPOSAL NUMBER: 98-1 19.08-9102

PROJECT TITLE: Remote-Field Eddy Current Techniques for Structural Damage Detection in Aging Aircraft

TECHNICAL ABSTRACT (LIMIT 200 WORDS)

Inspection of multi-layer metal structures such as aircraft is a technical challenge because of access restrictions, presence of fasteners, large sample thickness, and ultrasonic reflections at interfaces. Conventional eddy currents and pulsed eddy current techniques have been successful for limited sample thickness and defect dimensions. For increased defect sensitivities with thick samples (defects at depths greater than 12 mm from the accessible surface), the Remote Field Eddy Current (RFEC) technique shows promise. This technique has only recently been demonstrated to be feasible for flat plate structures. There has been no work in designing and studying the feasibility of using RFEC sensors for multi-layer structures with fasteners. During phase I of the proposed work, Karta will design and build a prototype of an RFEC probe specifically for optimal defect sensitivity to second-layer cracking of airframe fuselage structures. The effort will include experiments and modeling to estimate (1) maximum thickness of the outer layer through which RFEC can detect second-layer cracks and (2) crack dimensions that RFEC can reliably detect. In phase I, we will also develop an automated signal analysis scheme using neural networks. In phase II, we will study third-layer cracking, develop a field-demonstrable prototype, and incorporate probability of detection studies.

POTENTIAL COMMERCIAL APPLICATIONS

Technologies developed during this program have considerable potential for several applications, including inspections for aircraft (e.g., wing splice joints), naval (e.g. structural hull metal), space (e.g., structural space-shuttle metal), and utility industries (e.g., above-ground storage tanks). After an aircraft enters service, its structure must be inspected and maintained on an ongoing basis to ensure a continually high level of safety. This offers tremendous commercialization potential for both system sales and providing inspection services. Above-ground storage tanks are used in petrochemical industries for storing a variety of corrosive solutions. These tanks are typically single-walled or double-walled structures. The bottom of these tanks corrodes over time resulting in leakage. Wall thickness and roughness surface complicates inspection of the structures, especially in interpreting sensor signals. The RFEC technique seems to overcome some of these limitations and is an attractive method of inspection for this problem. Karta can focus on these two areas because of our strong understanding of the market. Once established in these areas, Karta will expand into other potential application areas including space and naval industries.

NAME AND ADDRESS OF PRINCIPAL INVESTIGATOR

Dr. Gopichand Katragadda
Karta Technologies, Inc.
1892 Grandstand
San Antonio , TX 78238-4507

NAME AND ADDRESS OF OFFEROR

Karta Technologies, Inc.
1892 Grandstand
San Antonio , TX 78238-4507