Set up and method

Dynamic testing

The ELVIS Gan Gun located at Cranfield University Shrivenham campus was used to conduct the experiments for this study. Full details of this gas gun and associated equipment used for this set up can be found within previous works by the same authors [14, 15].

The ball bearing was integrated to a plastic sabot, before being placed within the gun breach and closed. The High-Speed Video (HSV) camera and internal high-powered light were turned on prior to being gas gun being pressured to 12 bar of air (+/- 1 bar). Two light gates were used to accurately record the arrival time of the projectile and proven to deliver the projectile to the target at 235 ms− 1 (+/- 12 ms− 1). This velocity was chosen to align to previous Perma-Gel testing undertaken by A.Mabbott within the same research centre, whilst also considering the limitations on the Gas Gun [24]. Once pressurised, the gas gun was fired safely from a remote location. It should be noted that during the second stage of firings, the air used to run the Gas Gun was unavailable and therefore 8 Bar of Helium was used to achieve the same velocities.

Post firing, each sample was removed from the target chamber before being visually inspected for entry witness marks and permanent cavitation with observations noted. Where observations had been noted, these were subsequently validated using the HSV footage. Measurements of depth of penetration were undertaken using a steel rule which were later confirmed using the HSV footage to ensure no projectile withdrawal had taken place during temporary cavity collapse (by the rapid evacuation of air during elastic recovery), thereby falsifying the dataset. Based on repeat measurements by different operators, the uncertainty in the penetration measurement for this study is on the order of 0.5 mm.

The HSV camera used within this study was noted as a Phantom V12-12 with the settings provided in Table 3. This camera was used alongside the associated PCC software (version 3.11.11.806) to analyse projectile/material interaction including the measurement of projectile travel, wound cavity diameter, formation and collapse, shock wave transmittance, and any other observations of interest. To ensure this was done accurately, the camera was calibrated and values being noted (Table 3) to ensure appropriate scale setting was entered during post processing of the images and video. Additional post processing of the raw dataset outside of the PCC software was conducted using Microsoft Excel.

Phantom V12-12
Resolution = 1024 × 352
Frames Per Second = 33,000 fps
Exposure = 5.00µs
Calibration = 0.368 mm/pixel (Serial 1)Calibration = 0.363 mm/pixel (Serial 2)

Two serials were undertaken to generate data for this manuscript. Serial one was primarily focussed on creating a baseline understanding of the materials performance by investigating the projectile depth of penetration using the material ‘as delivered’, whilst the second serial focussed on assessment of the changes to depth of penetration caused by varying melt and re-cast cycles.