Automated Corrected MAR Calculation for Characterisation of AE Signals

Measured Amplitude Ratio (MAR) is a form of modal analysis for the classification of Acoustic Emission (AE) signals. MAR uses a comparison of the amplitudes of the first two primary lamb wave modes, symmetric (S0) and asymmetric (A0), to determine the orientation of the damage mechanisms in relation to the sensor. Previous researchers have demonstrated that some damage mechanisms, such as delamination in composite panels, inherently produce and outof-plane movement and so are expected to generate signals with an MAR value below one. On the contrary, other mechanisms, such as matrix cracking, have been connected to in-plane movements and so generate signals with an MAR value above one. Typically, the technique can consume much of the users time as it involves scrutinising many waveforms individually in order to record the amplitudes of their lamb wave mode constituents. Furthermore, due to the nature of each lamb wave mode to attenuate at different rates, the MAR of a single source might appear to be different depending on source to sensor distance. This problem is amplified in larger structures, where differences in lamb wave mode attention have more distance over which to diverge. An automated MAR calculation method that corrects for the attenuation of each lamb wave mode separately is proposed and discussed. The developed technique successfully differentiated sources of matrix cracking and delamination in a composite panel subjected to buckling. Results were validated post-test using c-scanning, digital image correlation and visual inspection.