Transition of energy release mode in confined internal explosions: The dominant role of structural confinement over material properties

Controlling the energy release from internal explosions represents a fundamental challenge in protective engineering. However, the relative roles of structural confinement and material properties remain insufficiently quantified. This study investigates the transition of energy release modes in confined internal explosions, with a focus on elucidating the relative influence of structural confinement versus material properties. A series of experiments were conducted on seven barrier configurations employing aqueous and polymeric materials under varying confinement conditions: partial, full, and reinforced. Multi-point free-field overpressure measurements, impulse witness-target, and synchronized dual high-speed imaging were employed to characterize the overpressure, impulse, and afterburning response. Results demonstrate that structural confinement plays a dominant role in governing the blast environment. Compared to partial confinement, a fully confined structure promoted a more uniform mass distribution around the explosive. It completely suppressed the negative overpressure phase and increased the specific overpressure inhibition efficiency by 25.1% per scaled mass. Furthermore, the highest confine degree significantly reduced the average impulse of gauges by more than 51%. Crucially, the afterburning effect was found to be more effectively suppressed by structural optimization than by the selection of materials with inherent flame suppression capabilities. A higher confine degree would transfer the energy release mode from a potential full afterburning into a partial mode. While adding foam to a water barrier delayed the leakage of explosive loads and improved energy conversion efficiency, the overarching finding confirms that the material-structure synergistic design strategy is significantly more effective than modifying material properties alone. Through rational mass redistribution, the total energy absorption of PU-C, PU-C_B, and PU-Cem_B was increased by 29.7%, 10.9%, and 59.6%, respectively, compared to the partial confinement case. These findings demonstrate the critical importance of structural confinement in controlling energy release modes and advance the development of collaborative material-structure design principles for enhanced protective structures.