Ultra-high speed on the single sound emission spectrum chara
Update time：2011-12-05 11:03 Viewed：次
Pick to: the threat of space debris impact spacecraft orbit perception system of development needs, to develop the perception system based on acoustic emission technique, it is necessary to study the characteristics of acoustic emission signal waveform hypervelocity impact. On the projectile hypervelocity impact experiment on the single aluminum, using ultrasonic sensor collected acoustic emission waveforms, and use wavelet transform to wave spectrum analysis. Results show that in 1 ~ 4 KMPS impact speed range, hypervelocity impact within the single board is mainly caused by acoustic emission wave A0, S0 and S2 model of elastic plate wave; Waveform weakened with the increase of impact velocity and A0 mode, the remaining two modes increases; Impact cratering waveform has stronger A0 mode, breakdown the impact wave has strong S0 models and S2. The introduction of the method in the process of hypervelocity impact to the concept of impact and radial expanding role, the rule is analyzed.
Key words: space debris; Hypervelocity impact; Acoustic emission; The wavelet analysis
0 the introduction
Due to the development of human spaceflight, has distributed a lot of space debris around the earth, and would naturally occurring micrometeoroid, brought enormous threat to the human space activities. If these with ultra high speed running of macroscopic particles on the surface of spacecraft, will cause serious and even devastation to the spacecraft. In this background, this paper proposes a using multi sensor network for monitoring and perception on the surface of the spacecraft, to this system, on the surface of the spacecraft by space debris impact of real-time monitoring, the resulting data will be to evaluate damage and launched the emergency plan of important information. So far, the plan put forward by the experts from all over the world covers many types of sensors. Type of piezoelectric acoustic emission sensor scheme with its mature technology, fewer spacecraft and rich impact access to information resource share, widely attention, foreign scholars for this type of piezoelectric acoustic emission sensor and the scheme of real-time monitoring technology is studied.
Acoustic emission sensor is used to analyse the impact of space debris monitoring and perception, its technology is based on principle of acoustic emission of hypervelocity impact phenomena. Traditional acoustic emission technology, mainly is the general failure of materials, structural mechanics environment fatigue, crack initiation and propagation, mechanical processing such as study mesoscopic phenomenon. In recent years, with the scope of application of acoustic emission technology, broaden the definition of the acoustic emission also expanded, has been widely put such as impact, turbulence, leakage and injection process induced stress wave in the structure into the category of acoustic emission, and using acoustic emission technology research. From a general point of view, for because of the space debris hypervelocity impact the phenomenon of spacecraft surface caused by stress wave release, can also be referred to as the "acoustic emission". But so far, the study of the ultra-high speed sound emission phenomenon is seldom reported. Prosser W to aim at hypervelocity impact impact load caused by acoustic emission wave is studied, and the actual use of ultra-high speed sound emission experiment testing, acoustic emission was observed with impact wave frequency peak speed transfer phenomenon. Schafer F using acoustic emission technology is described in the paper of space debris impact monitoring scheme, and locating by hypervelocity impact experiment technology application research. To sum up, the release of stress wave from hypervelocity impact can be considered to be a kind of acoustic emission phenomenon, and can use the concept of the acoustic emission method and technology were studied. Ultra-high speed sound emission phenomenon, however, after all is different from the sense of the acoustic emission, usually have different characteristics, the need for in-depth discussion.
Ultra-high speed sound transmitting wave contains rich information of wave propagation. By using two-stage light gas gun hypervelocity projectile hit single protective structure, through ultrasonic sensor to collect at a specific location to install acoustic emission signal waveform, and based on wave propagation theory, mainly by means of wavelet transform spectrum analysis was carried out on the waveform, to seek the characteristics of the ultra-high speed sound emission signal and its relationship with impact conditions and damage mode, for the space debris hypervelocity impact spacecraft positioning and damage model of quantitative evaluation technology foundation.
1 program
1. 1 laboratory equipment
High-speed high-speed impact of space debris impact experiments in Harbin industrial university research center of the secondary light gas gun HGG - 2. Targets adopted in the experiment for space commonly used 5 a06 aluminum alloy plate, the size is 600 x600mm, thickness of 5 mm. Experiments using the projectile diameter 3. 97 mm 2017 aluminum ball. Using secondary light gas gun, the projectile launched into six different speed, hit the target surface, the acoustic emission signal is produced by Panamatric2NDT V182 ultrasonic sensor, collected and recorded digital oscilloscope for subsequent analysis. Figure 1 is a photo of experimental equipment, figure 1 (a) is the secondary light gas gun, figure 1 (b) is already installed on the target of the target class. The whole experiment to simulate the main ingredients for aluminum alloy space debris hypervelocity impact on the surface of the particles on the spacecraft. The projectile velocity by magnetic induction log system, covering the scope of KMPS KMPS 1 to 4. The speed range of the impact, will make into a pit, spallation target board and breakdown of hypervelocity impact of typical damage model.
1. The choice of two sensors
V182 is used in ultrasonic thickness measurement used in the experiment of piezoelectric sensor, broadband sensitive type displacement sensor. Prosser M it is verified by experiment in 20 KHZ - 1. 5 MHZ frequency range is fairly flat response sensitivity, and further in the experiment waveforms collected by optical interferometer with linear displacement is compared, it was verified with a linear response of displacement [6]. V182 is not a special acoustic emission sensors, simultaneous launch sensor, compared with more flat frequency response, but lower sensitivity. Speed and acoustic emission sensor is usually sensitive, linearity is also poor. V182 these characteristics make it is adopted in the experiment, in order to get high fidelity waveform.
1. 3 sensor layout and the influence of the boundary
Experiments, the size of the target board as far as possible big, to ensure that the sensor collected waveform is not affected by the boundary reflection, but also for the waveform in the process of transmission sufficient dispersion provide sufficient time, is advantageous to the different modes and frequency waveform analysis. Target 5 a06 aluminum alloy plate material, the basic physical and mechanical performance parameters are shown in table 1.
By the theory of plate wave [10], board for the most part of elastic wave energy is focused on the compression wave and flexural wave, the former fast. By plane stress approximation theory of compression wave, compressional wave velocity is zero
According to the data estimation, plate wave velocity is the fastest in the 5. 53 KMPS. Set the impact point at the center of the target plate, the wave spread outward from this place and then be boundary reflected waves need to spread of 600 mm, the reason is installed near the center position sensors can be collected more than 100 us no boundary effect of waveform. However, considering the safety of the sensor to avoid more damage to the sensor signal even projectile itself, at the same time, considering the practical characteristics of spacecraft surface, collected the sensor can usually thickness more than several times the distance of the far field wave), sensors and waves keep a certain distance. The layout of the sensors in the experiments are shown in figure 2.
Set the target plate center as the impact position, four sensors distance here is respectively 150 mm, 200 mm, 300 mm and 370 mm. Volatility spread outward from a point of impact and boundary reflection waves to the distance of 150 mm sensor of a path as shown in figure 2, as shown in the dotted line in the total distance 505. 2 mm, can be collected more than 60 us borderless affects waveform.
2 the result of the experiment and analysis
2. 1 damage to the target board
Bullet velocity of the projectile and target plate damage data as shown in table 2. Into a pit of feature sizes using pit on the diameter of the flange, the characteristics of the perforation size with minimum aperture. Experiment Numbers for N1, N2, two hair its speed is low, the impact to target board into a pit, the pit diameter increased with the increase of impact velocity; Experiment number N3 ~ N6, the projectile velocity is higher, the target plate were breakdown, perforation diameter increased with the increase of velocity.
In order to further understand the waveform frequency components, the signal wavelet analysis. First of all, according to the wave arrival time to determine the time lag, which will be followed by small spectrum timeline for calibration. In this experiment, the waveform has rich high-frequency component, is very difficult to make sure the arrival time of the flexural, can clearly identify the compressional wave arrival time is adopted. According to the four sensors wave arrival time and distance is the actual position of the point of impact, fitting out of the compression wave displacement - time line, the slope of the line that the corresponding wave velocity, axial intercept instant of time
Between the delay, as shown in table 3. To experiment to get the waveform of wavelet transform, and table 2 of 5 a06 material parameter calculation of the 5 mm thick aluminum plate group velocity dispersion curve, and according to the measured time lag and sensors from the point of impact position, by adding to the small spectrum pseudo color graphics are as shown in figure 5 the wavelet spectrum of pseudo color graphics. Figure 3 is respectively has the cratering and breakdown two typical damage modes of the target board.
2. 2 acoustic emission waveform and spectrum analysis of wavelet
Experiment for 6 groups of waveform, its typical data as shown in figure 4. To compared with ordinary acoustic emission signal, break the lead of the acoustic emission standard calibration source waveform joined, as shown in figure 4 (a). Contrast figure 4 and figure 4 (b) (c), and low speed high speed cause breakdown of the waveform into a pit of waveform caused besides amplitude difference, also has obvious differences in the frequency domain: the former is given priority to with single frequency, only weak amplitude of high frequency components appear; While the latter waveform contains a strong high frequency component, make whole waveform frequency more rich. Contrast figure 4 (a), figure 4 and figure 4 (b) (c) can also be found: the hypervelocity impact wave arrives first part of the more obvious than the lead broken, will see below, this is S0 pattern plate wave of low frequency component.
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