The HOTM method for predicting ammunition response characteristics under different impact load conditions

With the development of modern weapon systems, the requirements for the survivability of ammunition in various complex environments have been continuously increasing. During the processes of storage, flight, and combat, ammunition may be subjected to extreme impact loads such as high-speed impacts, shock waves, bullet and fragment impacts. The external impacts can induce plastic deformation and fracture of the ammunition casing, and even detonate the internal explosives. These responses involve complex phenomena including impact loading, thermo-mechanical coupling of materials, chemical reactions of explosives, and blast effects, representing a typical dynamic response problem of reactive materials under extreme thermo-mechanical coupling conditions. Accurately predicting the responses of ammunition under impact loading is critical for its design optimization and safety assessment. Based on the Hot Optimal Transportation Meshfree (HOTM) method, a meshfree numerical approach was proposed to accurately predict the ammunition responses under different impact loadings. Meanwhile, a thermo-mechanical-chemical coupling constitutive model of explosives was established, which took the effects of temperature and pressure on the explosive’s chemical reaction and detonation into account. The Arrhenius thermal-chemical reaction coupling model for explosive initiation and the Lee-Tarver three-term pressure ignition model induced by local high pressure were integrated to accurately simulate the different initiation mechanisms of explosives under varying impact velocities, thereby predict complex physical phenomena during the impact loading of ammunition. These phenomena include high-speed contact, large plastic deformation of the metal casing, material fracture, heat conduction, explosive initiation, and the expansion work performed by chemical reaction products. Taking the numerical simulations of two typical impact scenarios—bullet impact on ammunition at 850 m/s and fragment impact at 1850 m/s—as examples, the influence of impact velocity on the initiation mechanisms of explosives and the overall response of ammunition was analyzed, with comparisons made against relevant experimental results. The proposed approach and findings provide reliable technical support for the optimization of impact-resistant design and safety assessment of ammunition.