Date of Award

2023

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering-Engineering Mechanics (PhD)

Administrative Home Department

Department of Mechanical Engineering-Engineering Mechanics

Advisor 1

Jason Blough

Committee Member 1

James DeClerck

Committee Member 2

Chuck Van Karsen

Committee Member 3

David Labyak

Abstract

In the aerospace industry it is known that performing shock analysis and testing on spacecraft is difficult to do mostly because shock loads create a very short duration shock wave transient that can have high acceleration peak levels (1,000-5,000 g) and wide frequency content (100-10,000 Hz). FE (finite-element) shock analysis is difficult because implicit linear FE software commonly used for most vibration analysis in aerospace does not account for shock wave propagation, reflection, and attenuation that occurs based upon the distance from the shock source at the base of the spacecraft and the attenuations that occurs through mechanical joints. Spacecraft shock failures can occur at high frequencies (700-3,000 Hz) which are difficult to get accurate FE modal results to at these higher frequencies because there will be hundreds of modes involved.

Subsystem shock test levels will have order-of-magnitude type errors at some frequencies vs other vibration predictions and subsystem test levels, like sine and random vibration, which typically have less than 20% errors at critical frequencies.

Smaller spacecraft are becoming more common. There is no acceptable or standard test method to test smaller spacecraft. As part of this work two different prototype mobile mechanical devices were developed and successfully used to qualify a NASA spacecraft mockup, which represents a small size spacecraft, to full shock levels.

Both impact testing and full level shock testing were performed on the NASA spacecraft mockup using a shock resonant plate. Impact testing simulated a low-level pyrotechnic shock transient that clearly showed shock wave propagation, reflection, attenuation, and amplification throughout the spacecraft. This was possible because it is unique to have so many shock-rated accelerometers mounted throughout a spacecraft, including on two simulators with different mass that represent spacecraft subsystems on multiple interior bulkheads. As a result, improved spacecraft subsystem shock levels used for subsystem shock tests were obtained.

As part of this work, a structural analyst will learn how to perform spacecraft impact and full-level shock testing and FE shock transient modal analysis, spacecraft FE model correlation, spacecraft subsystem impact and modal testing and analysis, and subsystem FE model correlation. This information in one document will provide guidelines and help create standard ways for performing shock testing and analysis. This should help address the commonly asked question in the aerospace industry - what do we do about shock loads? The key is to do more shock testing. Such guidelines and standards are needed because shock analysis and testing is much less commonly done than vibration testing on a shaker.

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