Dynamic Characteristics Of Energetic Materials Shield Induced By Hypervelocity Impact

With the increase of space activities,space debris density has increased continuously and caused a serious threat to the safety of the spacecraft.In order to meet the demand of all kinds of spacecraft protection,a variety of advanced protective structures were developed based on whipple shield by the United States,Russia and European space agency.Although many materials are applied to protective structures,they are all inert.In this dissertation,the impact-initiated energetic materials are firstly fabricated and applied to the space debris shield development based on the engineering application background of space debris protection design.PTFE/Al has been widely used in defense industry due to its high energy,insensitiveness,and unique characteristics of impact initiation.This dissertation introduced the optimizing process method and got a well material,which obtained better behavior at the material dynamic analysis.Hypervelocity impact tests,to study the damage properties and ballistic limit curve of PTFE/Al energetic material with space debris,were carried out by using two-stage light gas gun.Numerical simulation was added to analyze the debris cloud movement characteristics and reveal the protective mechanism of the impact-initiated Energetic Materials.We got the relationship between molding pressure,density and yield strength by changing the material molding pressure,sintering temperature curve,heating rate and sintering atmosphere.Preparation technology optimization was achieved by utilizing vacuum sintering and the sintering process curve that with melting and crystal platform,so that material density reached 0.95 and yield strength was 18.5MPa.To study the dynamic mechanical properties of PTFE/Al at high-low temperature,dynamic compression experiments were conducted by using a split Hopkinson pressure bar.The dynamic compressive stress-strain relations of PTFE/Al under the temperature between-100? and 200? at different strain-rates were obtained,and also constitutive model were got.The impact initiation process in SHPB were researched by High Speed Photography,and the relationship between initiating delay time and impact velocity was concluded,which could be used to demonstrate the change of initiating delay time along with the different impact velocities from low speed to high speed.Hypervelocity impact tests with different areal densities,projectile diameters,and impact velocitieswere carried out by using two-stage light gas gun combined with experimental measures of High Speed Photography,optical pyrometer and Laser Shadow Photography.Compared with LY-12 Al thin-plate with the same areal density,the effectiveness of PTFE/Al energetic material shield was proved.The damage characteristics of energetic material shield under hypervelocity impact were studied.A non-dimensional empirical expression for perforation diameter of the PTFE/Al bumper was established by dimensional analysis,while ballistic limit curve for the new material shield was achieved.The SPH code and material parameters were verified by experimental results.Debris cloud form of energetic material shield was obtained using the SPH code,and protective mechanism was investigated and revealed as well,from which debris cloud movement characteristics under different shield thickness was concluded.The fragmentation-initiation velocity equation of aluminum alloy projectile was set up.Furthermore,the impacts on hypervelocity impact characteristic of energetic material shield by the ambient temperature were investigated.The results indicate that ambient temperature has an influence on perforation on energetic material shield and has less effect on debris cloud movement characteristics.