Viscous motion of particles in shock-compressed epoxy*

Understanding the fluid response of materials at high pressure requires the characterization of transport properties such as viscosity. Here, we present an experimental measurement of the dynamic viscosity of Stycast 1266 epoxy, a common target material. The experiment was conducted at the Dynamic Compression Sector, where epoxy samples embedded with 20um tungsten particles were shock-compressed to ~4.5 GPa. High-speed radiography was used to capture the motion of the tungsten particles embedded in the epoxy. To determine the velocity behind the shock, 100nm-thick gold fiducials were placed in the epoxy. Radiographs were post-processed to determine particle position over time. Assuming that the shocked epoxy behaves as a Newtonian fluid, particle trajectories were predicted using Clift-Gauvin and Stokes drag models by iterating through various possible viscosity values; the theoretical trajectory that had the best fit to the data was used to determine the epoxy’s viscosity. Both models yielded a low particle Reynolds number (less than 1), so the Stokes drag assumption is likely appropriate.The Stokes drag model resulted in a dynamic viscosity of ~58 Pa.sec.