MULTIPHYSICS MODELLING OF COOK-OFF EXPERIMENTS

摘要

The overall objectives of this project were to built and assess multiphysics finite elements models for simulating cook-off experiments in both a small scale variable confinement cook-off test (VCCT) apparatus and a generic 105mm shell. The COMSOL Multiphysics modelling software was selected to obtain a numerical description of the tests geometry and then employed to calculate the time evolution of temperature and pressure within the test cell or shell for several energetic materials composition. This was achieved by simultaneously solving the equation of changes for momentum, heat and mass transfer. In the latter case, kinetics models were incorporated to reflect the early decomposition of the energetic materials found in the system. The following high explosive formulations, Composition B, PBXN-109, CX-85 and IMX-104, were simulated and the results were confronted to experiments conducted in GD-OTS Canada laboratories. Heat losses to the environment were accounted for by considering natural convection and radiant energy, using COMSOL's built-in correlations to estimate the local heat transfer coefficient. Additional details such as solid-solid contact thermal resistance, melting enthalpies and temperature dependant physical properties were also included. Whenever possible, the kinetics of the decomposition behaviour of the energetic materials used were obtained from DSC measurements using an isoconversional analysis method. Different heating rate cycles were simulated. For all geometries the analysis showed that simulated temperatures were close to experimental observations from thermocouples positioned on the samples and test cells. The estimations of time to onset of runaway reaction were also in good agreement with experimental data. As a whole, the study tends to confirm that a simulation approach could eventually be used as a screening tool to reduce the experimental workload associated with the assessment of thermal sensitivity of energetic materials.