Energy Conversion Prediction Model of Expansion Tube under Near-Field Blast Loading

The explosion near-field is the core zone of munition-induced damage, involving the coupled load effect of intense shock waves and detonation products. Currently, the mechanical response and energy conversion mechanisms of expansion tube structures (ETS) under such extreme loading conditions remain unclear. In this study, ETS is adopted as a representative energy-absorbing structure to investigate its energy conversion behavior under the coupled action of near-field shock waves and detonation products. Based on the experimental verification, numerical simulation methods were employed to analyze the characteristics of near-field blast loading and the dynamic response of ETS. Furthermore, a theoretical prediction formula for near-field blast loading was established, and a theoretical model for predicting energy conversion efficiency was developed based on the strong-shock assumption. The results show that the energy conversion efficiency decreases significantly with increasing scaled distance. The energy conversion efficiency drops to below 10% when the scaled distance exceeds 0.80 m/kg^1/3. Moreover, the energy conversion efficiency exhibits a strong positive correlation with the specific impulse of the reflected wave, indicating that specific impulse is a key factor determining energy transfer. This work elucidates the intrinsic mechanism of energy conversion in ETS under near-field coupled loading. The proposed theoretical model provides a robust foundation for the design and performance evaluation of near-field protective structures.