TECHNOLOGY AREAS: Materials/Processes, Sensors, Weapons

ACQUISITION PROGRAM: Office of Naval Research EM Railgun Innovative Naval Prototype (INP)

RESTRICTION ON PERFORMANCE BY FOREIGN CITIZENS (i.e., those holding non-U.S. Passports): This topic is "ITAR Restricted." The information and materials provided pursuant to or resulting from this topic are restricted under the International Traffic in Arms Regulations (ITAR), 22 CFR Parts 120 - 130, which control the export of defense-related material and services, including the export of sensitive technical data. Foreign Citizens may perform work under an award resulting from this topic only if they hold the "Permanent Resident Card", or are designated as "Protected Individuals" as defined by 8 U.S.C. 1324b(a)(3). If a proposal for this topic contains participation by a foreign citizen who is not in one of the above two categories, the proposal will be rejected.

OBJECTIVE: Develop non-destructive instrumentation for composite materials to enable structural health monitoring and advanced diagnostics.

DESCRIPTION: The US Navy is pursuing the development of an electromagnetic launcher (also known as a rail gun) for long range naval surface fire support. An electromagnetic launcher consists of two parallel electrical conductors, called rails, and a moving element, called the armature. Current is passed down one rail, through the armature, and back through the other rail. The armature is accelerated down the barrel due to the interaction between this magnetic field and current flow (Lorentz Force). An electromagnetic rail gun (EMRG) system will accelerate projectiles to hypersonic speeds, enabling ranges beyond 200 NM in less than 6 minutes of flight time while traversing the atmospheric spectrum (endo-exo-endo). The EMRG can address time-critical targets with a rate-of-fire of 6 to 10 rounds per minute while residual energy at target impact provides lethal effects.

One of the major design challenges associated with electromagnetic launchers is the need for a containment structure around the electrically conductive rails that can maintain the positioning of the launcher components even under the high electromagnetic forces and extreme tribological conditions associated with a launch event. Historically, these containment structures have been very large and heavy and have therefore posed an impediment to the operational utility of railguns. As a result, the Navy is developing new containment designs that utilize composite materials to significantly reduce the footprint of the containment while offering similar or improved performance relative to traditional designs. Composite materials, however, are not always compatible with existing diagnostic instrumentation and therefore advanced instrumentation is needed to monitor the health of these materials and to measure properties such as strain and temperature.

Although they offer superior strength relative to metals, composite materials also have the potential for sudden catastrophic failure under high loads. Composites are structurally anisotropic and also combine different materials phases, which means that detection of flaws and damage is a difficult task. Shock, impact, and repeated stresses can cause a variety of different effects including cracking, delamination of adjacent layers, and breaking of fibers, all of which can significantly reduce the strength of the material. The additional complexity of composite materials as well as the wide variety of damage mechanisms means that existing instrumentation is often inadequate to detect defects, determine the impact of identified defects on lifetime, or determine the critical size of damage. This effort will develop instrumentation that can address these issues in the composite structures used in an EMRG. There are a variety of different composite types in use or being considered for use in EMRG applications with thicknesses up to two inches, and any instrumentation must be compatible with these material types.

For railgun applications, the most critical diagnostic need for composite materials is non-destructive methods for evaluating the structural health of the containment before, during, and after a launch event. This capability must be able to detect damage or emerging defects in order to determine the safety of the containment structure on a shot to shot basis. In order to meet this requirement, the instrumentation must be able to detect all critical damage mechanisms in real-time and must be able to do so without the need to make any modification to parts of the EMRG after each shot. In addition, the structural health monitoring instrumentation must provide data required to predict the lifetime of launchers without the need to test them to failure through actual launch events. The instrumentation should provide quantitative data (location, defect size, etc) on the presence of any flaws (to include cracking, delamination, and broken fibers) in the composite structure prior to use as well as the evolution or emergence of such flaws during operation of the launcher. It is anticipated that eventually hundreds of shots will be fired using instrumented launchers to obtain the data required to predict lifespan.

In addition to structural health monitoring, there is also a need to characterize the thermal behavior of launchers that use composite containments. For EMRG applications that have higher firing rates (multiple shots per minute) there will be a large amount of thermal energy that must be dissipated from the launcher. The ability to obtain spatially-resolved temperature measurements from the rail/armature interface to the outside of the containment will provide the data required to understand these issues and evaluate potential solutions. Any temperature sensing technique must be non-intrusive and not susceptible to the high EMI conditions that occur during launcher operation. In addition, the sensors must be able to accommodate a very wide range of temperatures as the launcher may be near room temperature on its exterior and can be as high as 1200� C (or higher) at the rail/armature interface. Spatial resolution should be sufficient to provide accurate localization data for all temperature measurements and should also provide adequate sampling over the entire launcher to map the temperature profile as a function of time. Temporal response should be adequate to provide real-time temperature data during a shot and would ideally be at least 1 MHz to provide a capability to capture dynamic temperature events.

There are a number of different technologies that could potentially be used for this application, including ultrasonic inspection, eddy-current testing, acoustic emissions, laser ultrasonics, vibration analysis, and radiography. The awardee is encouraged to explore innovative technologies in these categories or others not listed in order to address one or more of the areas above. All proposed techniques must be capable of surviving the EMRG environment, which includes extreme electromagnetic fields, electrical currents, temperatures, and mechanical stresses. The approach must also be non-intrusive, not require modifications to the launcher beyond initial sensor installation, and must not involve any destructive testing. It must be noted that the 10m continuous composite overwrap structure will have two axial, large conducting metal rails internally which may enhance or prevent certain diagnostic techniques relative to signal penetration and/or interference.

PHASE I: Investigate sensor technologies that will provide the necessary capability to characterize the behavior of composite structures for electromagnetic launchers. Conduct bench-top tests of promising technologies to demonstrate their suitability for rail gun applications and ability to meet the requirements outlined above and identify any scaling issues that would be addressed during the transition to full scale testing. The outcome should be instrumentation that shows strong potential applicability to composite EMRG applications.

PHASE II: Design and fabricate prototype devices and test using a composite electromagnetic launcher or in another environment that replicates the EMRG environment. The outcome should be at least one device that has demonstrated compliance with the requirements above and that shows promise for full-scale testing in an EMRG. A design study should be performed to show the robustness of the concept in the full-scale EMRG environment that is outlined above. The results of testing may be classified.

PHASE III: Incorporate the instrumentation into an existing full-scale composite launcher. Perform open-range measurements using the existing launcher to demonstrate the capability developed complies with the requirements for composite diagnostics. The EM gun may be available as a government furnished test asset or through a teaming relationship with other EM gun test sites. If successful, work with Navy contractors to incorporate the instrumentation into advanced composite launcher concepts being developed by industry. If necessary, modify design to allow for use in an at-sea environment to enable transition to PEO IWS, PMS 405, ONR Program Office and integration with industry launcher manufacturers' production weapon systems that will be sent to the fleet.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The techniques that are developed could have application for a number of different commercial technologies that utilize composite materials. Because of their performance advantages and reduced weight, composites are increasingly being used for a variety of applications, especially in the transportation sector where future aircraft and automobile designs are comprised of high percentages of composites to reduce weight. As a result, sensor technologies that provide health monitoring and diagnostic capabilities for composites may also be used in the automotive and aviation industry for safety monitoring and non-destructive evaluation as well as for any structural diagnostic requiring high frequency response. The ability to predict structural failures and monitor critical system parameters such as temperature is an equally important capability for commercial applications as it is for Navy purposes.

REFERENCES:
1. Farrar, C.; Worden K., "An introduction to structural health monitoring", Philosophical Transactions of the Royal Society A, Volume 365, February 2007, Pages: 303-315.

2. Tzeng, J.; Zielinski, A.; Schmidt, E., "Design Considerations for Electromagnetic Railguns", J. Pressure Vessel Technology, Volume 128, Issue 2, May 2006, Pages 263-266.

3. Diamanti, K., Soutis, C., "Structural health monitoring techniques for aircraft composite structures", Progress in Aerospace Sciences, In Press, Corrected Proof, Available online 26 May 2010.

4. Silva-Munoz, R.A.; Lopez-Anido, R.A., "Structural health monitoring of marine composite structural joints using embedded fiber Bragg grating strain sensors", Composite Structures, Volume: 89 Issue: 2, June 2009, Pages: 224-234.

KEYWORDS: Electromagnetic launcher; railgun; composites; non-destructive evaluation; temperature

** TOPIC AUTHOR (TPOC) **

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