Research On Temperature-dependent Mechanical-chemical Response Of Single-compound Explosive And Composite Explosives

HMX(Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) and RDX(Hexahydro-1,3,5-trinitro-1,3,5-triazine)are two kinds of commonly single compound explosives.Composite explosives based on HMX and RDX have been widely used in the military for charge of missile warhead,fish and nuclear warheads.Studying the mechanical response of explosives under quasi-static,dynamic,and different temperatures is the key to understand detonation and safety performance.The mechanical properties of explosives under various conditions are obtained through experiments,and the corresponding deformation and failure mechanism were investigated,which is the basis of safety of explosives,weapon charge,and engineering applications.In this paper,starting with the mechanical behaviors of explosives under different loading conditions,the dynamic mechanical response of single compound explosives and composite explosives and their influences on their safety are studied.The mechanical properties of RDX-8701 were studied by using quasi-static compression and Hopkinson test technology,and thedesigned low-temperature and high-temperature loading systems.The quasi-static and dynamic stress-strain curves of RDX-8701 at the wide range temperature(-125??15?;15??100?)and the corresponding mechanical properties parameters were obtained.The fracture mechanism of RDX-8701 at different temperatures was analyzed using Scanning Electron Microscope.It was found that the fracture mode of RDX-8701 under quasi-static and lower temperature is mainly interface debonding along the binder,while the failure mode under the quasi-static and higher temperature is mainly caused by the softening of the binder.Under high rate loading,RDX-8701 shows a mixed failure mode combing interface debonding inside the binder with transgranular cleavage under low temperature,while the failure mode of RDX-8701 is mainly temperature-softening of the binder under high temperature.Using the modified drop weight impact machines equipped with low temperature controlling device as the main research methods,the impact response image and the ignition probability of the powder explosive under low temperature environment were obtained through high-speed camera.The theoretical model was employed to study the HMX powder explosive under drop weight impact.The calculation results show that the temperature of contact point between the HMX particle and the drop weight surface and that of the contact point between two HMX particles rise faster as the environmental temperature decreases.However,the temperature of contact point between the HMX particle and the drop weight surfacerise faster and higher than the temperature of the contact point between two HMX particles.This is because the main ignition mechanism of particle explosives under drop weight impact is friction.The frictional work of contact area between the HMX particle and the drop weight surface is greater than that of the contact surface between two HMX particles which leads tohot spots forming easily.According to the calculation results,it can be inferred that the hot spot mainly formed on the contact point between the HMX particle and the drop weight surface,and the peak temperature of the contact point rise higher as the environmental temperature decreases.The fragmentation of HMX/RDX large particles under drop weight impact is studied through experiment.The particle sizes of HMX/RDX fragments are analyzed to obtain the distribution curves and average sizes of fragments at different drop heights by using Malvern MS2000 laser particle size analyzer.The analyzed results show that,the sizes of fragments tend to be decreased with the height of drop hammer.However,when the height increase to a certain value,the fragments distribution curves are very close.Based on the experimental results,the theoretical formulas for the average size and fragment distribution of HMX large particles under drop weight impact were established.The morphology of explosive fragments was analyzed by scanning electron microscopy.More detailed mechanical-chemical response images of small particles during drop weight impact were obtained based on high speed photography.The frequency for high-speed photography was set to be 420000 frames/s and the resolution is 128~*48 pixels.Experimental observations proved that sputtering is a physical-chemical phenomenon,which is due to fragments motion pushed by gas generated once hot spots formed.Sputtering is caused by the formation of hot spots,but the formation of hot spots does not always cause sputtering.The particle size distribution of HMX has a great influence on ignition method.If particle size is larger than 1080?m,ignition is easy to occur in the solid phase.But when the particle size is less than about 700?m,ignition may occur in liquid phase and solid phase.When fine powder explosives are mixed with large particles(either energetic particles or inert particles),the hot spots are easily formed at the junction where the particles and the powder explosive are mixed,and the subsequent propagation of the combustion reaction starts at this interface.The mechanical properties of composite explosives are the results of the interaction of energetic grains and binders.The content of binders is small,but it has a great influence on the global mechanical properties of materials.A Mesoscopic calculation model was established to study the effects of RDX crystals and binders on the average mechanical properties of the composite explosive RDX-8701 at different temperatures.From the simulatedresults,it can be seen that as the temperature decreases,the stress of the RDX grains and binders increases with the strain.RDX grains play a leading role on the mechanical properties of RDX-8701,because the strength and content of the RDX is greater than that of binders.