TECHNOLOGY AREAS: Materials/Processes, Sensors

ACQUISITION PROGRAM: PMS 501, Littoral Combat Ship, ACAT 1

OBJECTIVE: To develop a light-weight, low-cost, reliable, sensor technology to enable the detection of heat sensitization and the resultant material degradation in 5XXX-series aluminum alloys onboard naval ships.

DESCRIPTION: Sensitization can be describes as changes in the chemical composition of the grain boundaries of a material. There is no visible loss of material (e.g. pitting, etc.) and little or no special chemicals on the metals surface. Current marine-grade aluminum alloys (5XXX-series) are commonly used in naval combatants and are known to be susceptible to sensitization. These aluminum alloys provide high strength-to-weight ratios while maintaining good as-welded strength and excellent corrosion resistance. However, alloys with above 3 wt% magnesium (Mg) are known to be susceptible to heat sensitization. At relatively low temperatures (~70�C) over long periods of time (10 - 20 years), the Mg diffuses to the grain boundary regions. When the local concentration of Mg is high enough, beta (ß) phase (Al3Mg2) forms. The ß phase is anodic to the matrix of alloy in seawater and this potential difference provides the driving force for dissolution of the from the grain boundaries, which then manifest as stress corrosion cracking (SCC) and exfoliation corrosion. SCC is common in sensitized, recrystallized, high-strength, marine, aluminum alloys in naval environments subjected to prolonged tensile stresses. Exfoliation corrosion affects sensitized, un-recrystallized plates and sheets in marine environments. Material degradation due to sensitization has been observed in the fleet in the form of SCC problems on the Guided Missile Cruisers (CGs) and exfoliation from the Vietnam-era Swift boats.

The ability to detect phase in commercial alloys onboard ship is therefore of great interest in order to find areas that may be especially susceptible to SCC and/or exfoliation corrosion. The current standard for detecting the degree of sensitization (DoS) in these materials is the laboratory performed, ASTM G67 Nitric Acid Mass Loss Test. However, this test is not amenable to field use due to the destructive nature and long exposure time of the test. Currently, there is no method of real-time, sensitization detection and in-situ monitoring.

This topic seeks to develop, affordable, light-weight, reliable, sensor technology to enable real-time, in-situ monitoring of heat sensitization and its related physical property degradations. Since the physical properties of the material systems being measured change slowly over time, sampling rates of 1 per minute are acceptable. The sensor(s) should be able to differentiate the DoS over the range of 5 to 50 mg/cm2 as determined by ASTM G67. The goal is to be able to assess an area of material of at lease 20 cm2. Incorporation of self powering (e.g., energy harvesting methodologies) for system power would be most beneficial. The sensor(s) should also be capable of operating in stressful operating environments such as high humidity and/or flooding, high temperatures, electromagnetic interference, etc. with minimal degradation of performance and should be compliant with current American Bureau of Shipping (ABS) and Naval Vessel Rules (NVR) standards (www.eagle.org). It is intended that the proposed technologies will be able to be either permanently installed as part of the platform construction or back-fitable in areas of known concern. Proposers should address the ability of the proposed sensor technology solution(s) to exhibit sufficient performance robustness for the ship�s life which is expected to exceed 30 years. It is envisioned that information gathered from these sensors will provide real-world raw data to better understand the degradation of the physical properties over time, to validate the models used to determine and predict structural health, and to alert the platform operators of potentially disabling or platform damaging events as soon as possible. Technologies proposed need to be compliant with open architecture design protocols to able to interface with navy data acquisition systems such as, but not limited to, the Integrated Condition Assessment System (ICAS).

PHASE I: Demonstrate the feasibility of the development of an affordable, light-weight, reliable, sensor technology to enable real-time, in-situ monitoring of heat sensitization and its related physical property degradations. As applicable, the feasibility demonstration should include or address the ability to determine significant deviations from expected conditions on a laboratory test bed. Develop an initial conceptual design and establish performance goals and metrics to analyze the feasibility of the proposed solution. Develop a test and evaluation plan that contains discrete milestones for product development for verifying performance and suitability.

PHASE II: Develop and demonstrate the prototype(s) as identified in Phase I. Through laboratory testing, demonstrate and validate the performance goals as established in Phase I. Refine design and develop a detailed concept of operation and projected capabilities including, as applicable: prototype descriptions, production drawings, interface specifications, operating sequences, emergency procedures, logistics support plan, weight breakdown, system cost estimates (both acquisition and lifecycle), and manning/Human Systems Interface (H.S.I.) requirements. Develop a cost benefit analysis and a Phase III testing, qualification and validation plan.

PHASE III: The small business will work with the Navy and commercial industry to complete any remaining qualification testing, construct full-scale prototype(s) and install onboard a suitable naval platform. Conduct extended shipboard testing.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Any structural monitoring system developed for Navy ships will have direct commercial applications in ferries and cargo ships as well as possible applications in both military and civilian aviation.

REFERENCES:
1. H. Sohn. C.R. Farrar, F. M. Hemez, D. D. Shunk, S. W. Stinemates, B. R. Nadler and J. J. Czarnecki, "A Review of Structural Health Monitoring Literature form 1996-2001," Los Alamos National Laboratory report LA-13976-MS (2004). http://www.lanl.gov/projects/ei/shm/publications.shtml

2. Stress Corrosion Cracking of Aluminum Alloys - www.key-to-metals.com/Article17.htm

3. Oguocha et al, "Effect of Sensitization Heat Treatment on Properties of Al-Mg Alloy AA5083-H116", Journal of Material Science, DOI 10.1007/s10853-008-2606-1.

4. Bushfield, Harold Sr., et al, "Marine Aluminum Plate ASTM Standard Specification B 928 and the Events Leading to Its Adoption". Presented at the October 2003 Meeting of the Society of Naval Architects and Marine Engineers, San Francisco, California.

5. Bovard, FS, "Sensitization and Environmental Cracking of 5xxx Aluminum Marine Sheet and Plate Alloys," Corrosion in Marine and Saltwater Environments II: Proceedings of the Electrochemical Society, ed. DA Shifler, 2004, pp. 232-243.

6. Searles, JL, et al, "Stress Corrosion Cracking of Sensitized AA5083," Aluminum Alloys 2002: Their Physical and Mechanical Properties Pts 1-3: Materials Science Forum, 396-4, 2002, 1437-1442.

7. ICAS Web site: https://icas.navsses.navy.mil/ (accessible without username/password)

KEYWORDS: structure; monitoring; sensors; collection; analysis; damage detection

** TOPIC AUTHOR (TPOC) **

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