Characteristic Analysis of Acoustic Emission Signals Caused by Debris Cloud Impact
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摘要: 为了掌握带防护屏的航天器结构受空间碎片超高速撞击时的声发射信号特征，利用二级轻气炮发射球形弹丸撞击铝合金双层板结构，获取了碎片云撞击铝合金板舱壁产生的声发射信号，并利用小波包技术和能量熵理论对信号进行了分析。实验结果表明：弹丸初始速度、防护屏厚度及弹丸直径是决定二次碎片云形态及声发射信号特征的重要因素；在本实验工况范围内，小波包能量熵值能够描述声发射信号频率的复杂程度；当弹丸初始速度处于破碎段(3~7 km/s)时，随着初始速度的增大，二次碎片云进一步细化，撞击产生的声发射信号幅值趋于减小、频率成分趋于复杂化，其小波包能量熵值逐渐增大；防护屏厚度对声发射信号的小波包能量熵值影响较大，弹丸直径对其影响较小。研究结果有助于实现对碎片云撞击舱壁结构的损伤模式识别。Abstract: In order to understand the characteristics of acoustic emission signals caused by hypervelocity space debris impacting spacecraft with shields, a two-stage light gas gun was used to launch sphere projectiles to impact an aluminum-alloy Whipple shield, the induced acoustic emission signals were acquired, and analyzed by wavelet packet technology and energy entropy theory.The experimental results indicate that, the initial velocity of projectile, bumper thickness and projectile diameter are important factors to decide the form of debris cloud and characteristics of acoustic emission signals.The wavelet packet energy entropy could be used to describe the frequency complexity of debris cloud impact signals.When the initial velocity of projectile increases in the broken section (3-7 km/s), along with which the projectile breaks more completely and the energy entropy of acoustic emission signals increases.Under the experimental conditions, the bumper thickness has greater influence on energy entropy values than the projectile diameter.The wavelet packet energy entropy is helpful to estimate the initial velocity of projectile and the maximum impact damage region, combined with the predicted curve from the Christiansen ballistic limit equation, the damage pattern recognition of the bulkhead could be assessed.
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Key words:
- debris cloud /
- hypervelocity impact /
- acoustic emission /
- wavelet packet energy entropy
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图 1 碎片云撞击信号获取实验示意图
Figure 1. Schematic of signal acquisition experiments for debris cloud impact
图 2 实验结果与预测曲线的比较
Figure 2. Comparison between experimental results and predicted curve from Eq.(1)
图 3 不同破碎程度碎片云撞击损伤结果
Figure 3. Impact damage caused by different levels of fragmentation projectiles
图 4 弹丸不同程度破碎形成的碎片云撞击声发射信号波形
Figure 4. Debris cloud impact signals by projectiles with different fragmentation degrees
图 5 小波包能量熵值随弹丸初始速度的变化
Figure 5. Wavelet packet energy entropy changing with initial velocity of projectile
图 6 距离板中心不同位置处信号的小波包能量熵值
Figure 6. Wavelet packet energy entropy versus velocity at different positions
表 1 实验工况及结果
Table 1. Experimental conditions and results
No. dp/
(mm)tb/
(mm)v/
(km/s)Dmax/
(mm)Damage of
the rear wall1 3.20 0.5 2.78 110 P 2 3.20 0.5 3.25 120 P 3 3.20 0.5 3.52 129 P 4 3.20 0.5 4.24 142 P 5 3.20 0.5 4.63 150 P 6 3.20 0.5 4.92 158 P 7 3.20 1.0 2.50 102 NP 8 3.20 1.0 3.05 126 P 9 3.20 1.0 3.65 133 NP 10 3.20 1.0 4.00 152 NP 11 3.20 1.0 4.45 159 NP 12 3.20 1.0 5.05 165 NP 13 3.20 1.5 2.81 120 NP 14 3.20 1.5 3.05 130 NP 15 3.20 1.5 3.73 148 NP 16 3.20 1.5 4.21 160 NP 17 3.20 1.5 4.46 165 NP 18 3.20 1.5 4.81 170 NP 19 3.97 1.0 2.65 120 P 20 3.97 1.0 3.25 138 P 21 3.97 1.0 3.57 148 P 22 3.97 1.0 4.15 160 NP 23 3.97 1.0 4.55 170 NP 24 3.97 1.0 4.85 180 NP 25 4.76 1.0 2.31 110 P 26 4.76 1.0 3.01 140 P 27 4.76 1.0 3.30 145 P 28 4.76 1.0 3.75 160 P 29 4.76 1.0 4.64 180 P 30 4.76 1.0 5.20 195 P Note: P－Penetration in the rear wall, NP－No perforated point in the rear wall. 
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