Counter-intuitive stiffness dependence and energy response mechanisms of hemispherical-shell-cored sandwich structures subjected to underwater impulsive loading

This study investigates the dynamic response and protective mechanisms of hemispherical-shell-cored sandwich panels subjected to equivalent underwater impulsive loading, utilizing a combined experimental and numerical approach. Systematic experiments were conducted varying the cell wall thickness (t) and cell radius (R), with results normalized to decouple inertial effects. The experimental results revealed a counter-intuitive detrimental stiffness effect: increasing the core stiffness (by increasing t or decreasing R) significantly exacerbated the panel deflection, exhibiting a negative inertia effect. Numerical analysis elucidated the underlying physics of this phenomenon from an energy perspective, identifying dual detrimental mechanisms arising in high-stiffness structures under strong fluid-structure interaction (FSI). At the input end, an excessively stiff core creates a "hard" boundary at the fluid-solid interface, which restricts the transient recession of the wet facesheet. This suppression of the FSI unloading effect results in amplified shock wave energy input. At the transmission end, the high-impedance core degenerates into an efficient conduit for stress wave propagation, channeling excessive energy to the dry facesheet and precipitating protective failure. Conversely, a moderately compliant structure achieves a critical balance between mitigating FSI energy input and maintaining sufficient load-bearing capacity, effectively localizing energy within the front components. These findings demonstrate that stiffness tailoring is critical for underwater protective structures, advocating a design paradigm shift from passive load resistance to the active control of energy input and transmission.