Experiments and analysis to measure strength of Mo, Nb and V at strain-rates of ≈10⁷/s using gas-gun driven Richtmyer-Meshkov Instabilities

Richtmyer-Meshkov Instability (RMI) experiments involve shocking an interface with initial perturbations between materials of different shock impedances to study the material response at high strain rates. After the shock, the perturbations will invert and grow, although they may arrest due to strength. Our RMI experiments involved targets made from three metals (Mo, Nb and V) with body-centred cubic crystalline structures, which had engraved sinusoidal perturbations on a free-surface to determine average strength at strain rates ≈10⁷/s. A gas-gun was used to fire a projectile at our targets and photon Doppler velocimetry (PDV) probes were used to measure the post-shock behaviour of the free-surface for impact stresses between 16 and 28 GPa. We used the peak velocity of the spike during inversion as our primary metric, which was found to vary between 850 and 1,850 m/s. Lagrangian finite element hydrocode calculations were compared to the data and were used to assess the performance of several strength models for each material. Further simulations were used to obtain an estimate for the strength from the experimental data and provide a basis for recalibrating the models.

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