FY18-C1 GRC Combined Structural Dynamic Testing Methodology for Large Non-Linear Structures

Testing spaceflight hardware is a vital, but time consuming and expensive endeavor. Traditional dynamic test methods presently require two separate tests; the first, a modal test performed on a seismic mass, and the second, a flight level verification test performed on a shaker table. The vision of this research is to combine two separate structural dynamic tests required for space hardware verification into one, and perform this test at flight levels. If engineers are fully successful in realizing this vision, it would force a paradigm shift in the way dynamic testing is accomplished not only in the aerospace industry, but also in other industries as well. In the modal test, typically a low level dynamic excitation is input into the hardware to excite the resonant frequencies, which are used to correlate the finite element model. The model is then used to accurately predict the hardware safety margins of a simulated launch. This approach is only accurate if the hardware behaves linearly. However, spaceflight hardware often exhibits non-linear dynamic behavior. Non-linear behavior causes the modal parameters to change depending on the level of dynamic excitation. Consequently, it is important to develop modal parameters at near flight levels. The goal of this research and development effort is to implement the game changing methodology of extracting fixed based modal parameters and dynamically test hardware to the flight levels in one test using a traditional structural dynamics lab setup.

The approach being applied is unique in that it has never been attempted using traditional vibration facility hardware. Few attempts have been made at applying this approach, and none have made it past simple bench top test campaigns. With the onset of more non-linear structures, extracting the structural dynamic properties of hardware at full flight levels can be challenging and time consuming. The industry needs to develop a more accurate and efficient approach so that spaceflight hardware can continue to be launched safety and confidently. The vision of this research is to address both this need and making dynamic testing more cost efficient. The near-term benefits of this R&D effort would directly apply to many upcoming projects scheduled to be tested at the structural dynamics lab at GRC such as a lunar rover concept, SAFFIRE, SLS, and ORION-MPCV. When this method is proven effective, it would revolutionize the way structural dynamic testing is done on hardware not only in the aerospace industry, but also in other non-related industries such as the automotive and marine industries for a very long time.

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