Application of Wavelet Transform to analyze acceleration signals generated by HVI on thin aluminum plates and all-aluminum honeycomb sandwich panels

Among all possible dangers, hypervelocity impacts on structures produce also a disturbance field, which results from the superimposition of vibrations originating on the impact point and then reflected at the target boundaries. Such disturbance environment is composed by waves of different amplitudes, frequency contents, speeds and directions of propagation. The aim of this paper is to characterize this complex environment, through the identification of its fundamental constituents using the Wavelet Transform analysis method, useful for studying transient phenomena, including wave propagation. Common signal analysis tools, like Shock Response Spectrum (SRS), cannot provide a good description of the physical behavior of such waves, nor they can differentiate between them since their frequency decomposition does not retain any time information. On the contrary, Wavelets associate a time information to the frequency content: each wave can be characterized by its frequency band and arrival time. Starting from both numerical and experimental acceleration data from impacts on aluminum plates and aluminum honeycomb sandwich panels, Wavelet analysis was employed to identify symmetric and antisymmetric waves. Moreover, reflections and dispersion phenomena were observed, leading to wave distortion due to different speeds of propagation of wave trains characterized by different frequency contents.