Capturing shock-driven dissociation of polymers and foams

Polymers, and polymer-based composites and foams are used extensivey in engineering and defense applications in a range of components including structural bodies and supports, insulating layers, and vibration and shock mitigation parts. In several applications, they may be subjected to impact and shockwave compression. Under these loading conditions, polymers have several features that differ from those of metals, including compression of network volume at low pressures, viscoelastic behaviors, and shock-driven dissociation. A novel equation of state methodology has been developed for describing the shock-driven decomposition of solid and porous polymers at moderate shock input conditions. Examples of the shockwave response of several polymers, and a comparison of historical metals-based equation of state approaches to the new methodology will be presented. Furthermore, this modeling approach has been extended to porous polymer foams, and revealed, through a large series of plate impact experiments, a phenomena we have termed "reactive anomalous compression." A striking feature of our results is the shift from densification to expansion of shock-driven reaction products as a function of initial porosity. Expansion with increasing shock pressure is most commonly associated either with shock heating due to pore collapse in chemically inert materials such as metals or exothermic decomposition (detonation) of energetic materials. We describe an unexpected admixture of these two effects: shock heating due to pore collapse, but expansion in conjunction with chemical reaction. Lastly, efforts to measure reactive wave structures in shock-dissociated polymers, and new x-ray based diagnostic techniques will be described.