Dynamic equivalent shear viscosity of copper with shock compression: An innovative approach based on photonic Doppler velocimetry

An experimental analysis scheme based on photonic Doppler velocimetry (PDV) is presented to derive equivalent shear viscosities from post-shock particle velocities behind perturbed wavefronts. All experiments were performed on a two-stage light gas gun. PDV was employed to capture the temporal evolution of post-shock particle velocities at various positions behind perturbed wavefronts, while the shocked region was analyzed within the fluid approximation model to explore the dynamic evolution of the free surface under perturbed shock waves. Eulerian fluid theory was adopted for further theoretical analysis. Combined with short-time Fourier transform, PDV-measured signals were converted into frequency-shift signals. Based on the inherent correlation between free-surface velocity and post-shock particle velocity, the post-shock particle velocities in experiments were obtained, which were further substituted into two-dimensional numerical simulation fitting results to inversely derive the equivalent shear viscosities. Within the experimental pressures ranging from 51 to 124 GPa, the equivalent shear viscosity of T2 copper was determined to be 2620–5110 Pa s. The reliability of the present results was further validated via the electric-pins perturbation method under matched shock-loading pressures of 54–121 GPa, which yielded viscosity values of 2530–4980 Pa s. No phase transition occurred in copper within the experimental pressure range, and the equivalent shear viscosity presented an increasing trend with rising shock-loading pressure within a single-phase region.