Research On The Mechanical And Chemical Properties Of Polyimide And Its Influence On Hypervelocity Impact Phenomena

The Polyimide (PI) is a typical complex high-molecular polymer of imidemonomers. It is well known for excellent properties as light weight, thermal stability,good chemical resistance, low electrical conductivity, large radiation resistance, hightensile strength, large elastic module, and so on. Due to the excellent properties,polyimides are widely used along with composites based on polyimide fibers in themanufacture of parts for aerospace technology, polyimide films located in the surfacelayer are used to protect the spacecraft’s electronic equipment from damage by lowtemperature in the space, and polyimide resin are used to produce the solar cell arrays.The mechanical and chemical properties of polyimide and its influedce on hypervelocityimpact phenomena are studied in the paper.(1) The equation of state (EOS) for polyimideu in high-pressure state is determinedwith the shock compress experiments. An equation of state is a thermodynamic equationdescribing the state of matter under a given set of physical conditions, and theMie-Grüneisen EOS is a widely used EOS for solid materials. In our research, the threekey parameters of the Mie-Grüneisen EOS based on the shock adiabat for polyimide hasbeen determined with two-stage light-gas gun experiments, i.e. the bulk speed of soundof polyimide c0=(2.62±0.22) km/s, the linear Hugoniot slope coefficient s=1.25±0.063for pressure less than50GPa, and c0=(2.26±0.26) km/s and s=1.41±0.043for pressurefrom50GPa to about1TPa, and the Grüneisen parameter at initial state of1.53. TheMie-Grüneisen EOS for polyimide is finally obtained, and the parameter values areproved reliable via the comparison of Grüneisen parameter value calculated from twodifferent theoretical models and the experimental data.(2)The differential scaning calarmeutry (DSC) experiments andpressure-thermogravimetry (PTG) analysis experiments for polyimide are performed.The reaction heat is determined as81.96J/g through the DSC experiments, and thechemical reaction kinetics parameters with different pressure for polyimide aredeterminded through the PTG experiments. Finally, the laws of the kinetics parametersare obtained.(3) With the PTG results, a pressure-related and temperature-related chemicalreaction model for polyimide is established. The Arrhenius model does not contain thepressure factor when describing the thermal decomposition of materials, our modelwhich based on the Arrhenius model has considered the pressure factor to describe thethermal decomposition of materials. Our model is more accruable to describe thethermal decomposition of polyimide in shock wave compression condition.(4) A chemical reaction dynamics algorithm is established. Chemical reactionsleading to changes in substance component, the form of the mass conservation equation is much more complex. The pressure, specific internal energy and the componentpercent are all change following the numerical simulation. The unit pressure, specificinternal energy and the component percent are obtained from the balance of pressure,temperature and energy in this paper.(5) A three-dimensional hydrodynamic code employing the SPH method withFORTRAN language is compiled, and the chemical reaction is considered by theprogram. When impact by hypervelocity flyers, the debris cloud of polyimide target inthe process of formation and movement entails significant chemical reaction and releaseheat, and the heat conduction may also have an impact on thermodynamic state ofmatter, however, there is no ready-made program can simulate this process except ourSPH code. Finally, two examples are calculated with the code to vertify the accuranceof the code.(6) The hypervelocity impact between Al flyer with different impact angle andimpact velocity and polyimide target is simulated by using the equation of state, thermaldecomposition kinetic model and SPH code. Influence of chemical reaction is mainlyconsidered, characteristics of debris clouds and penetration hole produced in the impactare presented, influence of the impact angle and impact velocity on the debris cloudsand the penetration hole are discussed, and the pressure distribution and temperaturedistribution are obtained. The results show that materials around the penetration hole areboth destroyed by the mechamical factor and thermal factor (such as thermal stability).