Session: 07-09-01: Vibrations of Continuous Systems

Paper Number: 119807

119807 - An Improved Technique for the Experimental Characterization of Small Impulses: A Space Technology Case of Study 

The experimental characterization of the impulse generated at the separation of two metallic surfaces, produced by the rupture of the adhesive bonds, presents a challenging research activity that spans the domains of system dynamics, experiment design, measurement techniques and mechanical vibrations modeling and measurement. Accuracy of impulse characterization is critical for the functionality of a launch-lock and release mechanism for a space application, since the space environment provides adhesion-critical conditions, sometimes leading to failure of critical mechanisms.  Therefore, the framework of space mechanisms is identified as particularly challenging for tribological aspects. A testing facility, based on a sensing body suspended in a nearly free-fall condition as a pendulum inside a vacuum chamber, has been developed in order to experimentally generate and characterize suitable impulses. Usually, the pendulum swing mode response constitutes the main observable for the estimation of the impulse, i.e. the time integral of the adhesion force time history up to the rupture of the bonds. In this research, the observable quantities correlated to the adhesion impulse characteristics are extended to the vibration modes of the suspended body of the pendulum, where the impulse is applied.   The modes of vibration whose period is close to the time duration of the impulse provide dynamically independent observables of the impulse itself, making it possible to achieve high accuracy of the estimated parameters. Moreover, the multiplicity of the outputs (amplitudes of vibration) produced by the same input (adhesion impulse) is exploited to characterize additional properties of the impulse, i.e. not only the adhesion force time integral but also the impulse time duration.

In this research it is demonstrated that such information may be disentangled from sources of noise and systematic effects present in the experimental facility. The technique hereby presented enables the exploration of the adhesive impulse's dependence on the applied preloading force between the adhered bodies. The vibration modes’ frequencies and amplitudes are obtained using both an optimal filter and a spectrum analysis based on a Fast Fourier Transform (FFT) algorithm. Various window functions are applied to minimize spectral leakage and improve the accuracy of the impulse characterization. Starting from the modes’ amplitude estimation, the proposed approach combines a numeric finite element model of the suspended pendulum and a dedicated symbolic dynamic model of its motion together with a fitting procedure, improving the estimation performance of the technique.

This enhanced characterization approach provides valuable insights into the behavior of adhesive bonds and facilitates a deeper understanding of their dynamical properties. The novelty of this approach can be summarized in three points. First, the research focus is on the impulse generated by the dynamical rupture of adhesive bonds, which is crucial for predicting the momentum acquired by a body when it is released to free-fall conditions. Second, the estimation of the adhesive pull gives information regarding the contact failure dynamics at large separation rates. Last, the approach relies on the modal response of the sensing body, which can be tuned to enhance the sensitivity of the experiment to given impulse intensity and duration and improve the rejection of noise and possible systematic effects.

Presenting Author: Edoardo Dalla Ricca Industrial Engineering Department - University of Trento

Presenting Author Biography: Edoardo Dalla Ricca received his master’s degree in mechatronics engineering from the University of Trento, Italy, where he is currently pursuing the PhD in mechatronics and systems engineering. His main research interests include the ground-testing of space mechanisms and the development of analytical models for predicting their dynamic response.

Authors:

Edoardo Dalla Ricca Industrial Engineering Department - University of Trento
Giuliano Agostini Industrial Engineering Department - University of Trento
Daniele Bortoluzzi Industrial Engineering Department - University of Trento
Carlo Zanoni TIFPA Trento Institute for Fundamental Physics and Applications
Dario Petri Industrial Engineering Department - University of Trento