铝合金平板超高速撞击声发射信号S2模态特征分析

对铝合金平板上形成的超高速撞击(HVI)声发射(AE)信号S2模态的特征进行研究，分析其与损伤模式之间的关系。以3 mm厚5A06铝合金平板为研究对象，通过数值仿真获得不同撞击工况下的超高速撞击声发射信号，提取信号中的S2模态，并分析其幅值、能量、频谱等特征。结果表明，S2模态能量随传播距离呈指数衰减；分别随撞击弹丸直径和撞击速度的增加先下降后上升，且在弹丸直径与靶板厚度相近、临界撞击速度时最低。S2模态的中心频率随弹丸直径的增加而降低；随撞击速度的增加而增加；随传播距离的增加向1500 kHz移动。S2模态小波包系数呈凹性的频域范围分别随撞击速度和弹丸直径的增大变窄。在此基础上，当靶板形成穿孔损伤时，可根据S2模态的中心频率推测弹丸的直径；在传播距离和弹丸直径已知的前提下，可根据S2模态小波包系数呈凹性的频域范围推测撞击速度。

Characteristic Analysis of the Hypervelocity Impact Acoustic Emission S2 Mode in Aluminum Plate

The characteristics of the hypervelocity impact (HVI) acoustic emission (AE) S2 mode in aluminum plate is investigated with the aim of researching the relationship with the damage pattern. A variety of HVI AE signals in different cases are obtained by the numerical simulation, with the research object of an aluminum 5A06 single wall plate, 5mm in thickness. The S2 mode of the signal is extracted to analyze its features of amplitude, energy and frequency spectrum. Results indicate that the energy of the S2 mode has exponential decrease with increasing propagation distance, follows a rule of decreasing firstly and then increasing with increasing the projectile diameter and impact velocity respectively, and finally reaches its lowest point with the ballistic limit velocity and diameter of the projectile approximate to the thickness of the plate. The center frequency of the S2 mode decreases with increasing the diameter of the projectile, increases with increasing impact velocity, and moves to 1500 kHz with increasing the propagation distance. The frequency range whose wavelet coefficient of S2 mode is concave, is narrow down with increasing the impact velocity and diameter of the projectile, respectively. And on this basis, the diameter of the projectile can be speculated by the center frequency of S2 mode if the hold damage appears, and the impact velocity can be speculated by the frequency range whose wavelet coefficient of S2 mode is concave when the diameter of the projectile and propagation distance are known.