Abstract

Vibration qualification testing is necessary to ensure that components will endure vibration-induced damage in flight. Multi-axis tests have shown the potential for improvement over single-axis tests, though they require increased planning. This work focuses on planning three critical aspects of these tests: the amount of operational next assembly to include in the test, the size of shakers to use, and the number of shakers to use. Next assembly selection is studied by varying the amount of next assembly included in the lab test, performing physical tests, and comparing the accuracy of environment reconstruction in each test. In doing so, a tradeoff between impedance, i.e., how well the boundary conditions of the lab test match those of the flight and environment, and controllability, i.e., how many shakers are required to control the lab setup, is revealed. Hence, more next assembly should be included if enough shakers are available to control it, and less next assembly should be included if fewer shakers are available. The required size of shakers is understood by predicting the required voltage of each shaker before the test. This is first done via dynamic substructuring, though a simplified approach, termed FRF Multiplication, is introduced here. The advantages of this approach are that it is mathematically simpler and does not require drive point FRFs at shaker connection degrees of freedom or even a finite element model (FEM) of the lab setup. It is shown to be a reasonable approximation when the drive point effective mass of the lab setup at each shaker location is much larger than the shaker's armature masses, when the calibration mass is much larger than armature masses, and when the shaker stinger mode is outside of the test frequency band. Finally, the number of shakers required to give accurate response reconstruction is studied. A modal framework is used to develop theory which is validated through simulated tests. The number of required shakers is found to equal the number of lab setup modes.

Degree

College and Department

Ira A. Fulton College of Engineering; Mechanical Engineering

Rights

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