TECHNOLOGY AREA(S): Space Platforms, Weapons

ACQUISITION PROGRAM: JSF Joint Strike Fighter

OBJECTIVE: Develop a physics-based algorithm for assessment of energetic material wear, failure, and decomposition while under vibration exposure for use in compressing service life vibration phenomena into an equivalent laboratory test.

DESCRIPTION: Vibration-induced stress and associated wear accumulation over time, as a result of the platform carriage environment, is one of the reasons weapon systems can fail to perform their intended function. In terms of evaluating the effects of the service-use vibration environment on weapon systems, it is preferable to conduct laboratory vibration testing in real-time to most effectively assess exposure consequences. However, in most instances, real-time testing cannot be justified based on cost and/or schedule constraints; therefore, it is common practice to compress the service life vibration environment into an equivalent laboratory test.

For vibration environments, which vary in severity throughout the service life of the weapon, the duration of the laboratory test environment can be reduced by scaling the less severe segments of the service use vibration environment to the maximum levels of the service use environment through use of an acceptable algorithm. If metal fatigue is a significant potential failure criterion for the weapon system within its service use environment, laboratory testing of the weapon system using maximum service use vibration levels to compress test times is an acceptable practice within strict limits; namely, test amplitudes should not be over-exaggerated / accelerated merely to achieve short test durations. Excessive laboratory test amplitudes may lead to unrepresentative failures, and create extreme design requirements rather than designing to actual in-service conditions, resulting in additional program cost or even program failure.

The most commonly used method for calculating a reduction in laboratory vibration test duration is the Miner Palmgren hypothesis which uses a fatigue-based power law relationship to relate exposure time and amplitude. The Miner Palmgren algorithm is based on metal fatigue only and does not support assessment of weapon system energetic materials (e.g., warhead explosives and rocket motor propellants). Because a laboratory vibration test compression algorithm does not exist for energetic material, current practice within industry and the DoD is to assess energetic materials under laboratory vibration test conditions using the Miner Palmgren algorithm. It is well understood by the energetic technical area expert (TAE) community that use of the Miner Palmgren algorithm is highly insufficient for energetic assessment of vibration exposure, and could result in erroneous service use suitability decisions leading to loss of life and equipment and failure to accomplish mission objectives.

PHASE I: Design, develop, and demonstrate feasibility of a physics-based algorithm for assessment of energetic material wear, failure, and decomposition while under vibration exposure for use in compressing service life vibration phenomena into an equivalent laboratory test. Conduct a feasibility assessment that will include identification and characterization of energetic material properties required for input to the algorithm. Sample materials will be available to Phase I awardees. Develop prototype plans to be developed under Phase II.

PHASE II: Based upon the results of Phase I, develop a prototype algorithm and validate its capability through analytical and experimental demonstrations. Analyses and experimental results should predict and validate wear, failure, and decomposition failure modes.

PHASE III DUAL USE APPLICATIONS: Conduct a full-scale vibration test on a tactical weapon energetic system such as a warhead or rocket motor. Conduct testing in at least two separate case scenarios: e.g., one test case will introduce an induced failure mode that can be progressively tracked and validated throughout testing; one test case will demonstrate successful energetic service life for a given lifecycle of vibration exposure. Transition the final product to appropriate users. The technology developed will benefit the private sector in terms of energetic concerns for space launch vehicles as well as contractor weapon system development and evaluation.

REFERENCES:

1. Environmental Engineering Considerations And Laboratory Tests, MIL-STD-810G w/Change-1, 15 April, 2014. http://everyspec.com/MIL-STD/MIL-STD-0800-0899/MIL-STD-810G_CHG-1_50560/

2. Hazard Assessment Tests For Non-Nuclear Munitions, MIL-STD-2105D, 19 April 2011. http://everyspec.com/MIL-STD/MIL-STD-2000-2999/MIL-STD-2105D_34120/

KEYWORDS: Accelerated Vibration Testing; Vibration Induced Damage; Energetic Wear, Failure, and Decomposition; Miner Palmgren Hypothesis; Energetic Material Properties; Physics-Based Algorithm