Development and characterisation of a sapphire material graded areal density ramp loading system

Abstract

A series of six shots were performed using a graded areal density quasi-isentropic loading (ramp wave) generation technique, this is in order to develop and validate a non-metallic materials capability which is compatible with the magnetic particle velocity gauge technique. Building upon previous work using rapid prototyped alumina flyers, this trial used machined sapphire components which offered superior material quality. The aim of this series was to observe the loading generated in a target using Het-V diagnostics at multiple spatial locations in order to determine the uniformity of the loading, and then to compare the results with Autodyn modelling. Six shots were fired on a single stage gas gun using several system variations at a velocity range of 200 to 700 ms−1. The ramp loading in a lithium fluoride (LiF) target was found to be approximately uniform in all cases using Het-V probes spaced over a ∼17 mm square central region. Comparison with 3-D Autodyn modelling was reasonable at the higher end of the impact velocities, but poor at the lower end. This is attributed to issues with the Johnson Holmquist sapphire strength/failure model parameters used which were not independently validated. Further experimental and modelling work would be of interest in order to inform a predictive design capability for the loadings generated by the system.