The Decomposition of some RDX and HMX Based Materials in the One‐Dimensional Time to Explosion Apparatus. Part 1. Time to Explosion and Apparent Activation Energy

A One‐Dimensional Time to Explosion (ODTX) apparatus has been used to study the times to explosion of a number of compositions based on RDX and HMX over a range of contact temperatures. The times to explosion at any given temperature tend to increase from RDX to HMX and with the proportion of HMX in the composition. Thermal ignition theory has been applied to time to explosion data to calculate kinetic parameters. The apparent activation energy for all of the compositions lay between 127 kJ mol⁻¹ and 146 kJ mol⁻¹. There were big differences in the pre‐exponential factor and this controlled the time to explosion rather than the activation energy for the process.     

CFD Cook‐Off Simulation and Thermal Decomposition of Confined High Energetic Material

The handling, storage and safety before deployment of explosives are major key issues that confront the ammunition industry. Precautions have to be taken not to cause premature detonations and fatal accidents by studying their thermal behaviour. Research has been conducted to investigate the thermal stability of some secondary explosives such as RDX, HMX and TNT and their response to thermal stimuli. For the fact that real experiment which involves large amount of explosives can be potentially dangerous, cook‐off numerical simulation and experiment has been regarded as the best method to analyse such thermal behaviour of explosives. Prominent among these researches involve experiment and numerical analysis such as ODTX, SITI, and DDT experiments. In this work, numerical CFD simulation will be executed for the thermal behaviour of TNT including cook‐off and thermal decomposition. The heating rates were varied for both slow and fast cook‐off cases. In view of these thermal decomposition reactions which mainly consist of kinetic parameters were factored in the numerical simulation as well as the critical thermodynamic physical properties. To effectively handle the reactions, UDF was employed. Attention was paid on the melting time to ignition of explosive, the location likely for ignition occurrence, as well as temperature distribution in the course of the heating process. CFD simulation results showed that the location of ignition was around the supplementary charge.     

The Effect of Cook‐Off on the Bulk Permeability of a Plastic Bonded Explosive

Plastic bonded explosives when exposed to prolonged heating environments undergo a variety of changes that affect their bulk chemical, thermophysical, and mechanical properties. During slow heating conditions, referred to as cook‐off, the thermal behavior of the polymeric binder plays an important role in the transformations of these composite energetic materials. The recently introduced Darcian flow hypothesis for PBX‐9501 implies that, during preignition, temperature gradients will lead to pressure gradients which in turn will drive convection of decomposition gases throughout the explosive, thus affecting ignition time and location. Here, we focus on the cook‐off behavior of PBX‐9501 and investigate its effects on bulk permeability to gases produced as a result of thermal decomposition. The concept of Darcian convection through porous media is defined and illustrated in detail by the derivation of the governing equations for a permeameter. Based on a systematic analysis involving: 1) our current understanding about binder behavior as a function of temperature, 2) the physics of the gas permeameter apparatus, 3) the concept of liquid drainage by gas, and 4) the experimental record of four permeameter experiments with cooked PBX‐9501, we conclude that samples heated up to 186 °C were not permeable in the Darcy‐flow sense.