Interpretable Acoustic-Emission Leak Detection and ED+MLE-Based Regional Localization in Thin Aluminum-Alloy Plates Under Vacuum Pressure-Difference Excitation.

Continuous gas leakage in thin-walled sealed spacecraft structures produces sustained broadband acoustic-emission (AE) signals from which reliable first-arrival picking is difficult. This study presents an interpretable two-stage workflow that decouples leak screening from regional localization. Experiments used a 500 × 500 × 2.5 mm 3A21 aluminum-alloy plate with eight piezoelectric AE sensors under 0.1 MPa pressure difference. Intact, circular-hole, and slit-leak conditions were each tested three times with a 0.5-1.5 s steady-state window. Leak screening employed the 20-200 kHz mean spectral amplitude (Hann window). A provisional threshold of 0.85, set from three intact records, separated all leak records from intact controls. Regional localization used relative logarithmic RMS amplitudes in an energy-decay plus maximum-likelihood-estimation (ED+MLE) cost function on a 10 mm grid. The equivalent attenuation coefficient, empirically selected as 2.3 m-1 using the 1 mm central-hole calibration case, gave a 10 mm grid error for that calibration demonstration. With this coefficient fixed, the four transfer conditions yielded mean localization errors of 19.6-45.7 mm. The results provide preliminary feasibility evidence for leak detection and regional localization under the controlled laboratory conditions investigated in this study. Further validation requires independent channel calibration, larger background datasets, leak-rate measurements, parameter-sensitivity analysis, and testing on more representative structures.