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.

Strain measurements using Fiber Bragg Grating sensors in Structural Health Monitoring

“…Other measurements are related to temperature and acceleration sensors and FBG sensor behavior analysis under traction and compression conditions. It is important to mention that the research in this project continues the researches related to structures health monitoring based on of active piezo sensors [14]- [16].…”

Qualification of PWAS-Based SHM Technology for Space Applications

“…The specific problem of the tests relates to the ability of the PWAS transducer to measure the modal behavior of the structure on which it is attached in the simulated harsh environmental conditions and with simulated mechanical damages. Consequently, a considerable amount of testing stages, EMIS records, data processing, and analytical assessments on damage identification were performed [5,6,[24][25][26][27][28]. The following types of specimens were subjected to the tests: (a) PWAS STEMINC SMD07T02S412WL transducers, (b) M-bond 610 Vishay epoxy adhesive, and (c) STEMINC PWAS transducers [26] ( Figure 1).…”

“…The strategy of the program was that, in the first stage of tests, the PWASs and DSs were tested using simultaneous environmental factors that are specific to outer space, see Figure 7, the case of disc specimen 127 [25]. Then, to characterize the influence of each factor on the EMIS signature, in the second phase the tests were developed with harsh environmental factors acting successively instead of simultaneously [28], see Table 4. Figure 6.…”

“…A compensation technique [26,28], in fact, a horizontal displacement of graphs, was used to obtain graphs in Figure 8b. As far as irradiations are concerned, they cause insignificant changes to EMIS signatures (Figure 8c).…”

“…From here and from the paper [31] came the idea of exploiting the entropy concept in identifying the damage. Thus, an entropy method for damage detection and the prediction was proposed [28,32]. Since the possible use of SLDV is very costly, we propose a simple method that uses the EMIS global signature.…”