Ramp Loading to High Pressures Using A Bed-of-Nails Impactor

The ability to deliver a ramp loading via gas gun plate impact experiments enables a significant expansion of the accessible regions of the EoS surface. In particular it is useful for probing off-Hugoniot states close to the material isentrope, and opens up the potential to deliver other, more complex loading paths. Methods for achieving this typically entail the use of a graded density impactor, in which the transition from low to high density along the impact axis produces a ramped input wave. Most techniques rely on the use of multiple materials to provide this density gradation, but the Bed-of-Nails (BoN) approach achieves the same results using an array of tapered spikes, supplying a variation in areal density from tip to base. Previous tests of the BoN design have been successful in generating a ramp, but these have generally been conducted at impact velocities <1.5 km/s. While these initial trials were successful in demonstrating the BoN concept, the applications for ramp loading are limited in this regime due to the similarity of the Hugoniot and isentrope at low pressures. A series of experiments have therefore been conducted using the BoN impactor at velocities up to 5 km/s to assess the effectiveness of the design at higher pressures, with multiple variants tested to ascertain how changes to the nail profile influence the transmitted wave structure.



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