Hybrid FEM-SPH Modelling of Shock Acoustic Emission Waves in Whipple Shields under Hypervelocity Impact

Hypervelocity impacts (HVI) caused by orbital debris and micrometeoroids pose major threats to spacecraft structural integrity. This study presents a numerical investigation of shock acoustic emission (AE) waves generated during HVI in two-layer Whipple shield structures. A hybrid Finite Element-Smoothed Particle Hydrodynamics (FEM-SPH) method was implemented in LS-DYNA to simulate a 4.035 km/s normal-incidence impact. The model incorporates Johnson-Cook plasticity with strain-rate and temperature effects, together with the Mie-Gruneisen equation of state to represent shock behaviour. Material and EOS parameters were adopted from validated literature for aluminium alloys under hypervelocity loading.Experimental validation was carried out using published two-stage light gas gun data [1], [2], where seven miniaturized piezoelectric (PZT) sensors recorded transient AE signals on the outer shielding layer. Three stress extraction strategies were evaluated: the MaxMin method, the 2nd Principal Stress method, and a directional Formula method based on in-plane strain components. Signal similarity was assessed using a combined metric of normalized cross-correlation and envelope correlation with equal weighting.The Formula method achieved the highest combined similarity score (0.8736), closely followed by the MaxMin method (0.8728), and both exceeded the literature reference score (0.7740) [1]. Impact localization using a probabilistic hyperbolic mapping (PHM) algorithm with seven sensors produced positional errors between 2.22 and 2.37 mm for all methods. The MaxMin method provided the best localization accuracy at 2.22 mm. The results provide a systematic assessment of stress-to-signal extraction strategies for reconstructing sensor-consistent AE responses in hypervelocity impact simulations.