N121-099 TITLE: Detecting Crack Nucleation/Damage Mechanisms In Sea-Based Aviation Environments

TECHNOLOGY AREAS: Air Platform, Ground/Sea Vehicles, Materials/Processes

ACQUISITION PROGRAM: NAVAIR 4.3 Structures Community; PEO(A), (T) and (U&W); NAVSEA PEO(Ships)

OBJECTIVE: Design and demonstrate an innovative crack detection approach in wet (aqueous) and dry (gaseous) corrosion environments under various stress fields and gradients supported by analysis formulations for underlying damage mechanisms.

DESCRIPTION: The understanding of crack nucleation in corrosive environments through a rigorous analytical and experimental basis is required to prevent progressive damage from occurring in naval structures thereby reducing the total ownership cost of any structural asset. This fundamental understanding will not only help achieve better structural and metal alloy design for new acquisitions but will also help identify immediate remedial actions for current corrosion and stress corrosion cracking problems in the existing fleet (e.g., F-18 and P-3 aircraft). To achieve both an analytical and experimental understanding of crack nucleation in corrosive environments, there is a need for the development of nondestructive evaluation (NDE) techniques to detect the onset of crack nucleation in all types of stress fields and stress gradients present in real geometries.

Various NDE techniques and sensors that have been developed over the last decade are primarily intended for macro-crack detection in inert environments rather than in corrosive environments. There are various sensors that are capable of sensing environmental parameters like pH/Cl-, but there are only a few that are capable of measuring the onset of corrosion events. Electrochemical noise techniques have been used with some degree of success to detect onset of localized corrosion such as pitting and crevice corrosion. The detection of localized corrosion, while useful, does not capture damage mechanisms of stress corrosion cracking and corrosion fatigue in naval structures. Therefore, a systematic analytical study to understand the damage mechanisms in play and development of techniques/sensors to detect crack nucleation under various stress fields and environmental conditions is needed. Such an analytical study should capture material degradation, both at global and local levels, in corrosive environments to provide a framework of damage mechanisms considering the crack tip chemistry and chemical kinetics at the micro scale level. To support and complement analytical efforts, techniques and sensors must be developed to detect crack nucleation in both wet (aqueous) and dry (gaseous) corrosive environments that can react with the base metal [e.g., Al 7075, 7050, Ti -6-4, HY-80 and HY-130 alloys] to establish some corrosion product. The design tool should be envisioned to work within a condition-based maintenance framework to provide prognostic and diagnostic capabilities.

PHASE I: Develop an analytical approach for measuring crack nucleation for various stress fields and gradients. Demonstrate the feasibility of the approach to different environments through critical tests using novel techniques to detect crack nucleation. Outline the steps needed for improving both analysis and sensor development efforts.

PHASE II: Fully develop the approach formulated in Phase I into different material such as Al 7075, 7050, Ti -6-4 and HY-80,130 alloys. Support analysis through critical tests using the proposed crack detection technique under a variety of service loads and conditions. Provide verification of the ability of the crack nucleation measurement in differing environmental concentrations.

PHASE III: Transition the technology to a suitable platform of US Navy interest, and successfully commercialize the developed sensor system and innovative technology to designers and manufacturers.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The developed analytical and sensor tool has the potential to transition to the commercial aircraft market and industry for the efficient design of airframe structures resulting in improved component reliability and life extension due to elimination of airframe corrosion.

REFERENCES:
1. Huston D. Structural Sensing, Health Monitoring and Performance Evaluation, Taylor and Francis: London, 2006

2. Muster TH, Cole IS, Ganther WD, Paterson P, Corrigan A and Price D "Establishing a physical basis for the in-situ monitoring of airframe corrosion using intelligent sensor networks" Proceedings of the NACE Tri-Services Conference (TSCC05), 2005

3. Vasudevan AK, Suresh S, "Influence of Corrosion deposits on near threshold fatigue growth behavior in 2xxx and 7xxx series aluminum alloys", Metallurgical and Materials Transactions 13-2, pp 2271-2280, 1982.

4. Papazian, JM et.al "Sensors for monitoring early stage fatigue cracking" Int. Journal of Fatigue, Vol 29, Issues 9-11, Fatigue Damage of Structural Materials VI, The Sixth Int. Conf. on Fatigue Damage of Structural Materials, Sep 2007, pp 1668-1680.

KEYWORDS: Corrosion; Crack Detection; Wet/Dry; Mechanical Stress; Nucleation; NDE

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