Thermal loading of explosives--finite difference method with time step reduction.
The method of simulation of heat transfer during thermal loading of energetic materials is introduced. The combination of the simple finite difference method with a time step reduction enables the quick and precise calculation of ignition times. The results are in accordance with published model data. The method was also used to simulate heat transfer during the slow cookoff test and the result agrees very well with experimental data.
The prediction of thermal stability of self-reactive chemicals
SummaryAn advanced study on the thermal behaviour of double base (boost and sustain propellant) rocket motor used in a ground to air missile has been carried out by differential scanning calorimetry (DSC). The presence of two propellants as well as the different experimental conditions (open vs. closed crucibles) influence the relative thermal stability of the energetic materials. Several methods have been presented for predictions of the reaction progress of exothermic reactions under adiabatic conditions. However, because decomposition reactions usually have a multi-step nature, the accurate determination of the kinetic characteristics strongly influences the ability to correctly describe the progress of the reaction. For self-heating reactions, incorrect kinetic description of the process is usually the main source of serious errors for the determination of the time to maximum rate under adiabatic conditions (TMRad). It is hazardous to develop safety predictive models that are based on simplified kinetics determined by thermoanalytical methods. Applications of finite element analysis (FEA) and accurate kinetic description allow determination of the effect of scale, geometry, heat transfer, thermal conductivity and ambient temperature on the heat accumulation conditions. Due to limited thermal conductivity, a progressive temperature increase in the sample can easily take place resulting in a thermal explosion. Use of both, kinetics and FEA [1], enables the determination of the reaction progress and temperature profiles in storage containers. The reaction progress and temperature can be determined quantitatively at every point in time and in space. This information is essential for the design of containers of self-reactive chemicals, cooling systems and the measures to be taken in the event of a cooling failure.
The Scaled Thermal Explosion Experiment
We have developed the Scaled Thermal Explosion Experiment (STEX) to provide a database of reaction violence from thermal explosion for explosives of interest. Such data are needed to develop, calibrate, and validate predictive capability for thermal explosions using simulation computer codes. A cylinder of explosive 25, 50 or 100 mm in diameter, is confined in a steel cylinder with heavy end caps, and heated under controlled conditions until reaction. Reaction violence is quantified through non-contact micropower impulse radar measurements of the cylinder wall velocity and by strain gauge data at reaction onset. Here we describe the test concept, design and diagnostic recording, and report results with HMX- and RDX-based energetic materials.