Experimental Investigation of Shock Wave Attenuation by Shock-Absorbing Material

Pressure loads caused by shock waves (SWs) are one of the greatest potential hazards in H₂ applications. In open spaces, the area of the shock front continuously increases due to spatial expansion. In confined geometries such as tunnels, the shock front always propagates with the same tunnel cross-sectional area. Friction and reflection on the walls are primarily responsible for the decrease in amplitude and momentum+ with increasing distance. How additional shock-absorbing material can attenuate SW is not yet fully understood. In this study, a special, unbounded, cube-shaped (0.55 m) combustion unit filled with 4 g of H₂ (stoichiometric in air) is ignited in the center of a 220 m³ container. The detonation inside the combustion unit emits a SW, whose propagation and reflection on the container wall are measured. The SW reflection behavior (amplitude and impulse) on the steel wall is compared with the reflection on samples with an area of 2 m² made of polystyrene, polyurethane foam, acoustic glass wool, and structured acoustic foam. Compared to the reflected SW amplitude from the steel wall, the reflected SW amplitude on the soft materials is reduced by up to 50%. No clear trend was observed regarding the influence of the thickness of the absorbing material on the attenuation of the sound wave amplitude, while the attenuation of the positive sound wave impulse increases with increasing thickness of the absorbing materials.