Control of gaps in technical structures during ground vibration testing

OBRABOTKAMETALLOV MATERIAL SCIENCE Том 20 № 3 2018 EQUIPMEN . INSTRUM TS Vol. 3 No. 2 2021 Figure 11 shows the distortion distribution of the portraits of oscillations of a vertical stabilizer. The increased transverse gaps were identified in the front attachment points of the vertical stabilizer. Spacecraft while designed are tested by means of the GVT. Results of the experiments are vital to prove quality of a fabricated vehicle and measure its vibration strength, including detecting manufacturing damage. Since the maximum vibrational loads occur during launching, the spacecraft are tested in a launch configuration. Figure 12 illustrates a design scheme of an unsealed satellite. Flat sandwich panels along with a carbon composite cylinder form a structural framework. Satellite equipment (antennas, solar batteries and etc.) as well as an astroplate with navigation sensors and orientation systems are located on the panels. To perform the GVT, the satellite is set on the adapter which connects the spacecraft with the launch vehicle. Fig. 12 . A spacecraft structure design scheme: 1 – an adapter; 2 – a panel; 3 – an astroplate; 4 – antenna reflectors; 5 – panels of solar batteries; 6 – an attachment point of a solar battery Fig. 11 . Gaps in the front at- tachment points of a vertical stabilizer. The local normal- ization of the distortions The several steps of the spacecraft GVT are carried out [29]. Firstly, the spacecraft is exposed to loading with low intensity to find out whether its dynamical properties are close to design ones or not. After that, normalized vibrational loads are applied to the spacecraft. During the loading, damage might occur and propagate, for example, interconnections become broken because of the gaps. The third step repeats the program of the first one. Taking into account how the vibrational parameters have changed: the resonance frequency and oscillation amplitude; high-frequency components occurrence and spectrum shift, one detects, locates and identifies the defects. The unsealed spacecraft while the GVT are exposed to wide-band harmonic and random acoustic vibrations. Figure 13 and Figure 15 illustrate how the gaps in the two spacecraft were detected by using the distortion distributions. It is essential to highlight that in the course of testing the driving vibration was sinusoidal and the frequency was altering logarithmically. Since the process is considered to be nonstationary, the time segments close to resonance frequencies were gathered to calculate the global distortions of the portraits of oscillations. The maximum distortion distributions were chosen among the calculated ones.