Investigation On The Characteristics Of Ignition Subjected To Low Velocity Impact And Burning Evolution In Cracks Of Explosives

Non-shock ignition and burning evolution are the two key processes for responses of weapon projectile filling under accidental situations.Since this two processes are quite complicated,the current understanding level has not match the requirement for weapon safety evaluation.Therefore,experiments,numerical simulations and theoretical analysis have been performed aiming at this two key processes.Our purpose is to understand the ignition mechanism of explosive under low velocity impact and the evolution law for combustion in explosive under non-shock ignition.The investigation results of this paper can deepen our mechanism understanding on the non-shock ignition mechanism and the complicated mechanical-heat-chemical coupling process for high intensity reaction of explosives,and provide data support for safety research on weapon projectile filling,which has very important military and scientific significance.In this paper,we use experiments,numerical simulations and theoretical analysis to carry out investigations,and have made the following progresses:1.Aiming at the mechanism of non-shock ignition of explosives,drop-weight experiments have been applied to investigate the dynamic responses of HMX granular explosives under low velocity impact.The results can be summarized as follows.At the early stage of loading,or for incompact collocation of granules,temperature rise at local area is mainly due to granular deformation.At later stage,or for dense collocation of granules,temperature rise is due to both granular deformation and friction.For single granule,friction is among fracture pieces,and for multi granules,friction is among different granules.2.Gas-solid coupling discrete element method have been set up based on the current solid discrete element method.Gas discrete element model,thermal conductive model and the Arrhenius reaction model are added to this new method,giving it the preliminary ability of simulating the whole processes of impacting,deforming,granula crushing,local temperature rising,ignition and combustion evolution for explosive under low velocity impact.Preliminary numerical simulations for ignition of granular explosives under low velocity impact have been performed using this new built method.And the simulation results are consistent with experimental results qualitatively.3.Aiming at the problem of burning evolution of explosive under non-shock ignition,experiments of burning in preformed single crack inside explosive under thermal ignition have been performed,and have obtained physical images and quantitative data for the whole process of crack burning.Results indicate that under confinement with high intensity,convective burning in sub-millimeter cracks of explosive can produce high pressure exceed 200 MPa,and the flame propagation speed exceeds 600 m/s.Qualitative comparison between different experimental results has also been carried out,giving the influence law of crack width and confinement intensity on burning evolution.4.Qualitative analysis have been performed for each stage in the process of crack burning in explosive,and theoretical analysis is carried out for the pressurization stage.Simplified theoretical model has been set up with the one-dimensional isentropic flow theory.With this model,crack pressurization has been predicted.The theoretical result is in good agreement with experimental result qualitatively,providing a theoretical explanation for understanding the pressurization behaviour in crack burning.