Insensitive high explosives: IV. Nitroguanidine – Initiation & detonation

Time resolved measurement of shock pressures in high explosives is possible with inexpensive composite carbon resistors. These resistors are embedded plane to the surface of a Plexiglas slab fixed at the end of the explosive. This configuration was used with gap test experiments with a 10 g donor charge. No initiation delay is measured in Seismoplast I (plastic PETN) up to a gap height of 10 mm PMMA (Plexiglas) due to the time resolution of the measuring system. From 10 mm to 22.5 mm gap height distances for detonation development up to 25 mm are found. For even greater gap heights a shock wave with decreasing amplitude occurs. The detonation development can be explained by the measured structure of the shock waves. Behind a first shock front with nearly constant pressure a second front propagates with increasing pressure which at last catches up with the first and then the pressure increases further up to the Chapman-Jouguet pressure of 160 kbar. At a gap height of 25 mm a stationary shock wave configuration with amplitudes of 20 kbar and 30 kbar was observed.

Time resolved pressure measurement of the initiation in gap test experiments

The Small Scale Gap Test is a relatively simple experimental tool to obtain a measure of the shock sensitivity of explosives. An evaluation of this test is carried out with use of a computer simulation. The simulated pressures in the water gap compare to experimental data and justify the obtained energy fluence in the shock wave versus distance in the water gap. The initiating shock pulse can be represented by an equivalent planar shock with an effective diameter of only 15 mm and a pulse duration of ≈1 μs. For the type of explosives that show some non-ideal behavior and that have a relatively large critical diameter, the initiation pressure might provide an inadequate value for the shock sensitivity. It is recommended that besides using a critical shock pressure criterion also a critical energy fluence criterion is applied to rank the shock sensitivity of explosives. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Evaluation of the Energy Fluence in the Small Scale Gap Test

In an effort to extend the modified explosive component water gap test [1–3] defined by the NATO standardization agreement (STANAG) 4363, several countries have investigated the shock sensitiveness of confined lead and booster components having a diameter less than 5 mm [4–8]. A pentaerythritol tetranitrate (PETN) based acceptor pellet is chosen as a reference with a height and diameter of 3 mm. The height of the steel confinement is equal to the one of the HE pellet and the wall thickness varies. A 1-mm thick wall makes the component more sensitive (larger water gap). As the wall thickness is increased to 2-mm, the gap increases a lesser amount. A decrease in sensitivity is observed with a 3.5 mm thick wall (smaller water gap). This decrease of the water gap has been reproduced experimentally. This unusual behavior remains puzzling and does not allow the test to be extended for small components. This work presents the numerical simulations performed with LS-Dyna in 2D axi-symmetrical and 3D wedge configurations, using an ignition and growth model [9] for LX-16 (96% PETN, 4% FPC 461) in order to evaluate the shock sensitiveness for a confined HE acceptor.

Shock Desensitization Effect in the Confined Explosive Component Water Gap Test Defined by the NATO Standardization Agreement (STANAG) 4363

The Small Scale Gap Test is a relatively simple experimental tool to obtain a measure of the shock sensitivity of explosives. An evaluation of this test is carried out with use of a computer simulation. The simulated pressures in the water gap compare to experimental data and justify the obtained energy fluence in the shock wave versus distance in the water gap. The initiating shock pulse can be represented by an equivalent planar shock with an effective diameter of only 15 mm and a pulse duration of � 1 ms. For the type of explosives that show some non-ideal behavior and that have a relatively large critical diameter, the initiation pressure might provide an inadequate value for the shock sensitivity. It is recommended that besides using a critical shock pressure criterion also a critical energy fluence criterion is applied to rank the shock sensitivity of explosives.

Full Paper Evaluation of the Energy Fluence in the Small Scale Gap Test

By means of shock-wave measurements it was possible to calibrate the BICT-gap test. The relation between the height of the gap and the shock-wave peak pressure at the end of the gap is described. From other considerations the range where the test can be used, can be obtained. BICT-gap test will be used to test explosives whose critical diameters do not exceed 20 mm and which will be initiated by shockwave pressures from 7 kbar to 60 kbar. The test method can be regarded as a small scale-gap test for military explosives.

R. Wild

Papers

Shock‐Wave measurements in water for calibrating the BICT‐Gap Test