Measurement of the Mie-Grüneisen equation of state for polyimide

An equation of state (EOS) is a thermodynamic equation describing the state of matter under a given set of physical conditions, and the Mie-Grüneisen EOS is a widely used EOS for solid materials. Polyimide is a typical complex high-molecular polymer of imide monomers which is widely used in the manufacture of parts for aerospace technology and for fabricating the inertial fusion energy shells (IFE). When a spacecraft collides with a meteoroids (or orbital debris) or the IFE shells are radiated by high power laser, the polyimide used in the equipment is in high pressure state. In order to study the safety of the spacecraft and IFE shells, the EOS of polyimide should be determined. In our research, the three key parameters of the Mie-Grüneisen EOS based on the shock adiabat for polyimide have been determined with two-stage light-gas gun experiments, i.e. the bulk speed of sound of polyimide is determined as 2.62±0.22 km/s, the linear Hugoniot slope coefficient is determined as 1.25±0.063, and the Grüneisen parameter at initial state is determined as 1.53±0.135. The Mie-Grüneisen EOS for polyimide is finally obtained, and the parameter values are proved reliable via the comparison of Grüneisen parameter value calculated from two different theoretical models using the experimental data.