Propagation of acoustic emission signals in metallic fuselage structure

A study of the propagation of acoustic emission (AE) signals through metallic aircraft fuselage structure is presented. It was found that only the fundamental modes: A₀ and S₀ in a low frequency band, centred at about 70 kHz, exhibit long-range propagation. In this low-frequency band the fundamental modes exhibit low attenuation in all the waveguide systems that are likely to be encountered in metallic aircraft. Metallic fuselage structure features a high density of joints between the skin and support structure and numerical modelling indicated that these modes have an energy transmission efficiency of about 70% across a typical joint. This is supported by experimental data. Such efficient transmission over a succession of joints contrasts with that found at higher frequencies, where previous work found that the interference of modes with similar phase velocity inhibits long-range propagation. Such `mode twinning´ does not occur in the frequency range around 70 kHz, and so efficient propagation of AE signals is possible