Research On The “hot Spot” Model Of High-energy Explosive Shock Initiation And The Detonation Performance Of Aluminum-containing Explosives

Explosive is an important energetic material for development of national defense,industry and economy.Shock initiation of high explosives and detonation mechanism of explosives with high energy density are most interested by the researchers.Multi-scale of physical and chemical processes are involved in the shock initiation of condensed heterogeneous explosives,which is usually recognized to be caused by "hot spot"phenomenon."Hot spot" development is related to propagation of shock waves and the subsequent dynamic process,and the research on "hot spot",especially the compressible effects,is far more enough.Depending on the excellent detonation heat and working power,aluminized explosive has been the most widely used explosives with high energy density.However,aluminized explosive exhibits an unique non-ideal detonation process due to significant thermodynamic differences between aluminum and CHNO component,and the non-ideal detonation mechanism is still not clearly.This paper investigates the developing of shock-induced "hot spot" in compressible condensed heterogeneous explosives.Based on the generalized Hook’s law,a compressible"hot spot" model was proposed by solving the partial differential collapsing equations of compressible elastic-viscoplastic hollow sphere.The influence of shock compression on "hot spot" growth could be studied by "hot spot" reaction degree,which is computed by the new model and it is proportional to the strength of "hot spot" effect.The result shows that partial input energy is transferred into compression internal energy through bulk compression,while part of the rest input energy is transferred into thermal energy through viscoplastic deformation.The thermal energy is deposited near the inner surface mostly where the "hot spot" grows.Since the heating effect of compression internal energy is very little comparing to that of the thermal energy,the "hot spot" reaction degree becomes less upon a stronger shock compression.The computed results of new model shows that the "hot spot" reaction degree increases initially and then decreases as the shock pressure increasing from 1～10GPa.It also could be found that the "hot spot" reaction degree increases with an increasing initial porosity and a decreasing initial particle size of heterogeneous explosivesThrough thermodynamic calculation of aluminum and explosive components in aluminized explosives behind shock wave,it exhibits that velocity and temperature of explosive components are much higher than that of aluminum.Relying on the velocity and temperature disequilibrium between aluminum and explosive components,this paper introduced a new two-components method to study detonation velocity of aluminized explosives.The new method is a closed system of 12 algebraic equations and 12 unknowns,and the detonation velocity of aluminized explosives containing various size and fraction of aluminum can be solved precisely by numerical codes.The detonation velocities predicted by the new method were compared with experimental data of multiple RDX-,HMX-,NM-and TNT-based aluminized explosives,and the results present that average calculation deviation is less than 1%on the condition of aluminum fraction varying from 0～50%,and aluminum size varying from 500nm～150μm.The new model is much more precise than any other models regarding detonation velocity computing,and it demonstrates that heat absorption of aluminum within detonation zone has significant effect on the detonation velocity.Furthermore,the detonation velocity of RDX/LiF explosives is also calculated by the new model and the computing error is less than 1%,which displays a excellent additional ability of the new model to predict the explosives with non-metal additives.To research the secondary reaction of aluminum in post-detonation of aluminized explosives,systematic Φ25mm tube tests of RDX/A1(aluminum fraction is 15%and 30%,and aluminum size is 2,10 and 50μm),RDX/LiF(LiF fraction is 15%and 30%,and aluminum size is 3 μm)and RDX were made,and outer wall velocity of approximately 30 μs was recorded.A secondary burning code of aluminum was introduced into Dyna-2D program,and a new method to simulate the tube test of aluminzied explosives was proposed based on this code.Both the experiments and calculations demonstrate that the secondary reaction rate of aluminum is a decreasing function of aluminum fraction and size.Through the combined reaction model,diffusion mechanism and kinetic mechanism within the secondary reaction process was researched,and it shows that reaction of aluminum particles larger than several micrometers is controlled by the diffusion mechanism,while that of the smaller particles is controlled by the kinetic mechanism.In order to obtain the ignition delay of aluminum in the detonation flow,the data of～25mm tube tests of RDX/LiF and RDX/A1 were processed.The results proves that the ignition delay of aluminum increases as aluminum content and size increase.Under the condition of 15%and 30%content of aluminum,the ignition delay of 2μm、10μm and 50μm aluminum particle is approximately hundreds of nanoseconds,one microsecond and several microseconds,respectively.A convection ignition delay model was made on the assumption of aluminum igniting at its melting point,and the preliminary predicted time was in good agreement with the experimental ignition delay,which validates that aluminum in the detonation flow ignites at the melting point.