New results concerning structural health monitoring technology qualification for transfer to space vehicles

Abstract

This article reports the results of recent complex tests on the survival, in view of space applications, of structural health monitoring (SHM) methodology that uses piezo wafer active sensors (PWAS) and the electromechanical impedance spectroscopy (EMIS) method. Successive and then concomitant actions of the harsh conditions of outer space, including extreme temperatures and radiation, were simulated in a laboratory. The basis of the method consists in the fact that the real part of the bonded PWAS impedance spectrum, the so-called EMIS structure signature, follows the resonance behaviour of the structure vibrating under the PWAS excitation and, consequently, the onset and progress of structural damage with fidelity. The tests were conducted on the PWAS separately and aluminium discs with PWAS bonded on them as structural specimens. The conclusion of the tests is that the cumulative impact of severe conditions of temperature and radiation did not result in the decommissioning of the sensors or adhesive, which would have meant that the methodology was compromised. This conclusion occurs as a result of applying two new analysis methods to EMIS signatures. The first method, based on systematic observation of EMIS signatures during tests, makes it possible to distinguish between real damage with a mechanical origin and false damage, which is reversible and caused by the harsh environmental factors. A second method, based on the concept of entropy, shows how to identify mechanical damage at a certain distance from the PWAS. Moreover, an offline analysis of the EMIS “entropy” signatures supports the conclusion that the SHM technology survived the harsh environmental conditions.