Response Reconstruction of Unmeasured Subcomponents using Impedance Matched Multi Axis Testing

Abstract

Environmental verification testing is used to ensure that a structure can survive the random vibration conditions that it is expected to experience during its operational life on a vehicle. Current industry standard methods for this testing will attach the subcomponent of interest to a stiff plate on top of a large single axis shaker. The subcomponent is then excited to an overly conservative single axis profile since the real environment is often unknown. Additionally, the difference in connection geometry that the subcomponent experiences between the shaker and the vehicle will alter the dynamics of the subcomponent. Finally, ignoring the off-axis motion is unrealistic as most environments will not be restricted to motion in a single axis at a time. The combination of these effects is that the stresses during the test do not replicate the environmental conditions, and the test is a poor representation of the actual environment. This thesis explores a new verification testing methodology based on a combination of the Transmission Simulator Substructuring Method with the Impedance Matched Multi Axis Testing method to try and verify the survival of a subcomponent in a given environment without having the truth data from that environment on that subcomponent to use as an input to the test. The transmission simulator is used to maintain the same connection geometry between the subcomponent and the rest of the vehicle such that the dynamics of the subcomponent are better maintained between laboratory and the environment. Impedance matched multi axis testing is then used to recreate the full environment on the transmission simulator in all axes at once. Since the connection impedance between the transmission simulator and the subcomponent is the same and the transmission simulator matches the environment, the motion going into the subcomponent should match the motion from the environment and produce an accurate reconstruction test. Two experimental test cases are presented: the first was performed in two dimensions to develop the capabilities to perform MIMO tests and evaluate the results objectively, and the second was to thoroughly explore how well the methodology functioned on a multi axis assembly with a realistic environment. Finally, a simulated test case was presented to determine the best-case results using the methodology and to guide future experimentation. These cases gave evidence to prove that the transmission simulator based IMMAT testing was able to reconstruct the desired environment with moderate accuracy, however, the ability of the methodology to extrapolate the environment away from the transmission simulator is very sensitive to the geometry selected for the transmission simulator.