Investigation Of The On-orbit Sensing Technology For Typical Sturctures Subjected To Space Debris Impact Based On Acoustic Emission

With the development of human spacecraft, space debris became a threat to the spacecraft. As a response, people have developed protection programmes such as mitigation, active dodge and protect from space debris. However, due to technical and economic conditions, the threat from space debris impact still exists on the spacecraft, space debris impact sensing technology had immediate application equirements for manned spacecraft. The on-orbit sensing technology based on acoustic emission had application prospect for monitoring event moments, source location, damage pattern recognition and damage degree evaluation. The existing research results achieved how to determine the impact event occurred and source location in aluminum alloy plate, but pattern recognition and damage degree evaluation had not be achieved. And as the important application of on-orbit sensing technology, manned spacecraft capsules were usually aluminum stiffened plates and the important parts were added protective shield. Compared with plate, the characteristics of acoustic emission impact signals and signal propagation in the structure were more complicated. The relevant research work were less and needed to be further studied.Under such background, spherical projectile were used to simulate space debris, respectively impact single-layer aluminum alloy plate and dual-wall structure, aimed at the questions such as the characteristics of acoustic emission signals caused by hypervelocity impact, source localization, damage pattern recognition and damage degree evaluation. For aluminum alloy single-layer structure, the effect of projectile velocity, size and plate thickness on the impact acoustic emission signal characteristics were analyzed, the size of stifferners effect on signal propagation law and characteristics were analyzed. For aluminum alloy dual-wall structure, the effect of projectile impact parameters and dual-wall structural parameters on the characteristics of the secondary debris cloud impact signal were investigated. On this base, the schemes of source location and damage pattern recognition for single layer plate and dual wall structure were investigated. This paper mainly includes the following:First, aluminum alloy plate, aluminum alloy stiffened plate and aluminum alloy dual-wall structure were designed as targets, hypervelocity impact experiments platform and signal acquisition system were designed, the hypervelocity impact damage effect and signals were obtained. By using SPH simulation of hypervelocity phenomena, finite element models were set up to obtain acoustic emission signal. By comparing experimental and simulation of damage and the impact of the target signal waveforms, the effectiveness of numerical simulation experiments was verifed.Secondly, the relationship between the characteristics parameters of acoustic emission signal and the projectile impact parameters, target plate geometric parameters were established. Through experimental and numerical simulation of hypervelocity impact experiments, the characteristics of acoustic emission signal caused by projectile hypervelocity impact aluminum alloy plate were analysed based on lamb wave theory and wavelet transform, the influence on the characteristics of acoustic emission signal by projectile initial velocity, diameter and plate thickness were discussed. Based on the numerical simulation and lead break experiment, it were found that the stiffeners had little effect on the wave propagation velocity of S0 mode. But the signal amplitude were attenuation when the signal through the stiffeners, high frequency components of signal amplitude attenuation faster than low frequency.Thirdly, the relationship between the characteristics parameters of acoustic emission signal and projectile impact parameters and dual-wall structural parameters were established. The characteristics of damage and its acoustic emission signal caused by the secondary debris cloud impact plate, and the relationship between them were investigated. According to the acoustic emission signal frequency distribution, based on wavelet packet and entropy principle, the characteristic parameter wavelet packet energy entropy were built. The researches showed that the initial velocity of projectile, bumper thickness and diameter of projectile had influence on the degree of damage, the characteristics of acoustic emission signal closely related to the degree of damage and the damage area. The wavelet packet energy entropy of debris cloud impact signal could be used to show the degree of projectile fragmentation, and then to estimate projectile velocity.Fourthly, location methods for projectile impact aluminum stiffened plate and debris cloud impact plate were proposed. According to the characteristics of acoustic emission signals, the advantages and disadvantages of signal arrival time determination were analyzed. Experimental results showed that in comparison with the the traditional threshold method, the first peak were used as the arrival time of signal could reduce the error of wave velocity. In addition, debris cloud impacted localization programme were given by experimental and theoretical analysis. Using time difference of arrival location algorithm debris cloud impact damage centre could be given, and debris cloud damaged area were predicted by the establishment of empirical equation.Fifthly, the damage pattern recognition method based on neural network for projectiles hypervelocity impact single layer plate were proposed. Based on hypervelocity impact experiment and numerical simulation, the feature parameters used for damage pattern recognition and estimating the diameters of the projectile were analyzed. The neural network used for damage pattern recognition and estimating the diameters of the projectile were built up. The pattern recognition and evaluation of damage degree for projectile hypervelocity impact single layer plate were achieved.Finally, the damage pattern recognition method based on ballistic limit curve for projectiles hypervelocity impact spacecraft with shield were proposed, the schemes for dual-wall structural were given. Acorrding to the acoustic emission signal on the bumper, the diameter of the projectile could be estimated by using neural network, acorrding to the debris cloud impact signals on the target, the velocity of the projectile could be estimated through the signal wavelet packet energy entropy, combined with the impact limit curve of dual-wall structure, the pattern recognition and evaluation of damage degree were achieved.This paper studied the characteristics of acoustic emission signals caused by space debris impacted the typical structure of a spacecraft bulkhead. And discussed in detail source localization and damage pattern recognition process of projectile impact single-layer and dual-wall structure. The results had showed great value for the development of acoustic emission on orbit monitoring technique.