This paper aims to study the difference of results in breakup state judgment, debris cloud and fragment characteristic parameter during hypervelocity impact (HVI) on large-scale complex spacecraft structures by various numerical simulation methods. We compared the results of the test of aluminum projectile impact on an aluminum plate with the simulation results of the smooth particle hydrodynamics (SPH), finite element method (FEM)-smoothed particle Galerkin (SPG) fixed coupling method, node separation method, and finite element method-smooth particle hydrodynamics adaptive coupling method under varying mesh/particle sizes. Then based on the test of the complex simulated satellite under hypervelocity impact of space debris, the most applicable algorithm was selected and used to verify the accuracy of the calculation results. It was found that the finite element method-smooth particle hydrodynamics adaptive coupling method has lower mesh sensitivity in displaying the contour of the debris cloud and calculating its characteristic parameters, making it more suitable for the full-scale numerical simulation of hypervelocity impact. Moreover, this algorithm can simulate the macro breakup state of the full-scale model with complex structure and output debris fragments with clear boundaries and accurate shapes. This study provides numerical simulation method options for the follow-up research on breakup conditions, damage effects, debris clouds, and fragment characteristics of large-scale complex spacecraft.
The post-detonation burning effect of aluminum (Al) powder plays an important role during the expansion of detonation products (DPs) of aluminized explosives (AEs). Lithium fluoride (LiF) is an inert substitute for Al, and hence, a comparison of the performance of composite explosives based on cyclotrimethylenetrinitramine (RDX), such as RDX/Al and RDX/LiF, clearly illustrates its contribution to accelerating ability due to Al oxidation. A series of metal plate tests is conducted to measure the velocity history of a metal plate driven by RDX/Al and RDX/LiF through a photonic Doppler velocimetry system with 5%, 15%, and 25% Al or LiF contents. The detonation and expansion process of the AEs is generally divided into two stages: the detonation zone (DZ) and the post-detonation zone (PDZ). In the DZ, the Al powder remains inert, while it absorbs the detonation energy from pure explosives. Therefore, the equivalent inert dilution model is established and the equivalent inert dilution coefficient of the Al powder is introduced. In the PDZ, the Al powder reacts with DPs, and the Al oxidation reaction results with a change in entropy related to the reaction degree of the Al powder. Based on the local isentropic assumption, as well as the function of the reaction degree of the Al powder, a non-isentropic model is established. The method of the non-linear characteristic line is applied to theoretically calculate the metal plate velocity based on the non-isentropic model. In addition, the theoretical results show good agreement with the metal plate test results with an acceptable error (less than 10%), indicating that the non-isentropic model can be effectively applied to analyze the accelerating ability of the AEs.
Nowadays, aircraft fuel tanks are protected by measures such as inerting, fire and explosion suppression, which significantly improve their ability to mitigate mechanical damage and prevent fire in the case of an accidental attack. In this study, an equivalent inert fuel tank with fire and explosion suppression was designed according to the vulnerabilities of a typical fighter. Then, a ballistic gun, a 37 mm gun and a two-stage light-gas gun were used to propel different fragments in tank damage experiments at different speeds (1400 m/s–2600 m/s). Experimental results show that the disassembly of a fuel tank is a prerequisite for igniting fuel. When the fragments hit the gas phase of the tank, the fuel tank was not disassembled and the fuel was not ignited. The calculation results show that the internal oxygen concentration was always lower than the limiting oxygen concentration (12%) before the fuel tank was disassembled. In addition, the minimum ignition speeds of inerted fragments with different masses as predicted by the ignition criterion when hitting the liquid fuel are consistent with the test results. This shows that increasing the mass of inert fragments will increase the minimum ignition speed and reduce the probability of ignition of the fuel. However, the implosion effect of the energetic fragments released about 3 times the chemical energy of its own kinetic energy, and the high-temperature and high-pressure products were very beneficial to the disintegration and ignition of the fuel tank compared to inert fragments.
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