Development of a flyer design to perform plate impact shock-release-shock experiments on explosives

Two shock-release-shock plate impact experiments were performed on HMX-based explosive targets using a 50 mm bore single stage gas gun. The shock-release-shock magnitudes were approximately 2.5-1.0-4.3 GPa. Prior to these shots a series of inert experiments was performed in order to develop the flyer design. The initial configuration consisted of a single crystal NaCl front flyer separated from a sapphire rear flyer by a vacuum gap, but preliminary shots impacting an array of piezoelectric pins revealed that the front flyer bent when unsupported. Therefore 0.2 g/cc polyurethane foam was used to support the NaCl front flyer and generate the rarefaction fan. The input pulse generated in an inert target was recorded by impacting a PCTFE target containing an embedded manganin gauge, in order to verify the design. Magnetic particle velocity (PV) gauges were used to study the response of the explosive targets to the input shock. The measurements were subsequently compared with the results from a hydrocode implementing the CREST reactive burn model. The explosive was not observed to detonate, as it would in response to a single sustained 4.3 GPa pulse and the magnitude of the reactive growth was significantly lower than that predicted by the model. However, there was evidence of reactive growth building at the shock front of the re-shock, behaviour which is not observed following double shock loadings of comparable shock magnitudes without the intermediate release [1].