TECHNOLOGY AREAS: Materials/Processes, Sensors

ACQUISITION PROGRAM: PMS 397 OHIO Replacement Program, ACAT I

OBJECTIVE: The objective of this topic is to develop an innovative structural health monitoring (SHM) system capable of detecting damage in submersible non-pressure hull composite structures. Such a system must be capable of detecting damage underwater while withstanding high levels of vibration and pressure. The goal of this project is to develop a system to successfully detect and characterize damage in non-pressure hull submersible components in the challenging underwater environment. The overall performance and geometry of the base structure cannot be degraded through the use of the SHM system. Integration of sensors and electronic within the matrix of the composite can be considered as part of an overall intelligent structural design approach.

DESCRIPTION: The use of advanced composites is becoming increasingly common for submarine components. Benefits of composite structures include reducing the overall weight and total ownership cost. While the initial design and fabrication expenses of composite structures may be increased from traditional materials (steel or aluminum), the possibility for significant reductions in maintenance and fuel expenditures while increasing the time of duty will lead to an overall cost benefit. Composites also allow for increased flexibility in design, leading to more favorable material properties and thereby increasing the operational performance of a vessel. The advanced materials used are designed to withstand normal loading due to submersion and wave impact. However, even with component testing, these composite structures will never be subjected to every environmental or operational condition before use in actual service. Therefore, the ability to detect changes or damage to an in-service composite structure could significantly reduce the amount of mechanical testing required, the time to implementation, and the tendency to overdesign such components. The aim of this program is to develop a structural health monitoring system capable of detecting and characterizing (size and location) damage in submersible composite non-pressure hull components. Many SHM techniques and systems have been developed for use on a variety of structures. The goal of this program is to determine which of these techniques is suitable for submerged Navy composites. Finding small amounts of damage in a harsh environment over the life of the component, while also considering the survivability of the sensors and SHM system itself, are main developmental areas for this topic. The main sources of damage would be fatigue or direct impact, causing cracking or delamination of the composite material. Shock or even more severe sources of damage should also be considered a possibility. Even though the vessels are designed to reduce flow noise, and thereby cavitation, there might also be secondary concern for cavitation erosion in select areas. While in service, a SHM system applied to composite structures would decrease operational costs by reducing the amount of scheduled inspection and maintenance. The system�s sensors must be capable of operating in extreme environments including shock, high vibration (fatigue), high pressures, and a submerged environment. The system could also be extended for use on conventional materials subjected to the same rigorous environmental conditions. Necessary sensors and actuators may be either embedded in or surface mounted on the structure, but neither may reduce the design performance. A successfully developed SHM system will be capable of detecting small amounts of damage to a composite structure in normal operational environments.

PHASE I: The contractor must develop a concept SHM system to detect damage on an underwater structure. Proof that this system is viable will be shown on a self-developed composite prototype, allowing for sensors to be embedded if so desired. The contractor will then demonstrate damage detection and characterization capability with the composite specimen placed underwater.

PHASE II: Expand upon the Phase I work to develop a representative prototype capable of deployment for damage detection on an actual submerged structure subjected to representative loading conditions. The prototype will then be demonstrated under these conditions (such as pressure or operational cyclic loading and thermal gradients).

PHASE III: Integrate developed system with end user systems and interfaces. Conduct final experimental testing on actual naval assets. Transition damage detection of structures into both damage prognosis and damage mitigation.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: A number of other applications and industries would benefit from a submersible SHM system. The system could have potential benefit to any Navy application where damage is likely in a wet, corrosive, or underwater environment. Commercial shipping and tourism could also benefit from a successfully developed SHM system.

REFERENCES:
1. Mouritz, A. P., Gellert, E., Burchill, P., and Challis, K., 2001, "Review of Advanced Composite Structures for Naval Ships and Submarines," Composite Structures, Vol. 53, No. 1, pp 21-42.

2. Adams, D.E., 2007, Health Monitoring of Structural Materials and Components, John Wiley & Sons, West Sussex.

3. Farrar, C. R. and Worden, K., 2007, "An Introduction to Structural Health Monitoring," Phil. Trans. R. Soc. A, 365, 2007, pp. 303-315.

4. Farrar, C. R. and Lieven, N. A. J., 2007, "Damage Prognosis: the Future of Structural Health Monitoring," Phil. Trans. R. Soc. A, 365, pp. 623�632.

5. Sohn, H., 2007, "Effects of Environmental and Operational Variability on Structural Health Monitoring," Phil. Trans. R. Soc. A, 365, 539�560.

6. Sohn, H., Farrar, C. R., Hemez, F. M., Czarnecki, J. J., Shunk, D. D., Stinemates, D. W. & Nadler, B. R., 2003, "A Review of Structural Health Monitoring Literature: 1996�2001," Los Alamos National Laboratory Report
LA-13976-MS.

7. Farrar, C. R., et al. 2003, "Damage prognosis: current status and future needs" Los Alamos National Laboratory Report LA-14051-MS.

8. Shull, P. J., 2002, Nondestructive evaluation theory, techniques, and applications. New York, NY:Marcel Dekker, Inc.

9. Bar-Cohen, Y., 1986, "NDE of Reinforced Composite Materials�A Review." Materials Evaluation, Vol. 44, pp. 446-454.

KEYWORDS: Structural Health Monitoring; SHM; Composites; Submersible Structures; Sensors; Damage Detection; Smart Structures

** TOPIC AUTHOR (TPOC) **

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