Abstract:

Addressing the threat of frequent low-velocity impacts during the service of low-altitude aircraft， clarifying the mechanisms of damage accumulation and load-bearing degradation in composite sandwich structures is of great significance for enhancing their damage tolerance design. This study focuses on woven/unidirectional （UD） hybrid composite sandwich panels with honeycomb and foam cores， systematically conducting repeated low-velocity impact and Compression After Impact （CAI） experiments. The research primarily analyzes the dynamic mechanical responses and energy dissipation laws of these two typical sandwich configurations under consecutive impacts. Furthermore， the influence of face sheet stacking sequences on the damage modes and energy absorption characteristics is investigated， revealing the degradation laws and damage modes of residual load-carrying capacity. The results demonstrate that the woven layers effectively distribute impact loads and suppress micro-crack propagation. The core configuration governs the damage accumulation laws， which further dictates the buckling evolution and collapse modes of the composite sandwich structures under compressive loading. Specifically， the honeycomb sandwich structures undergo shear plugging failure under repeated impacts and exhibit transverse tearing cracks during subsequent CAI loading. In contrast， the foam cores exhibit a compression-shear coupled indentation failure mode through localized crushing and densification， offering superior residual load-carrying capacity compared to the honeycomb structures. This research provides a critical engineering basis for the anti-impact design and damage tolerance assessment of composite sandwich fuselage structures for low-altitude aircraft.

Key words: composite sandwich structures, woven/unidirectional hybrid, repeated impacts, Compression After Impact (CAI), failure modes