Computational Aided Engineering Tools for the Design of Thermites-based systems – OASYS

Reactive materials are composites or physical mixtures that demonstrate self-sustaining exothermic reactions upon receiving an initial energy input. This category of materials is distinctive within the realm of energetic materials, differing from explosives in the manner in which reaction fronts propagate subsonically and rely on atomic diffusion or other physical transport mechanisms. This dependence on transport mechanisms allows for the engineering of reactive materials to exhibit reactions over a broad range of timescales, depending on the length scale of the reactants.

Over the past 20 years, metal based reactive materials such as thermite have brought much hope to power future generations of miniature autonomous systems and to provide high-energy actuations within smaller volume (cm3). They are benign, harmless to the environment and chemically safe, yet highly energetic, reacting at extremely high-temperature combustion in all environments even in deep-sea or in harsh-environments. They can therefore provide tunable actuations for the protection of collectivities, for antitamper devices and systems, or for maneuvers in-space or welding repairs underground in geothermal or in disaster-stricken areas, which are not possible with any other traditional energetic materials.

However, the e?ective transfer of such promising materials, which emerged in 90s from research laboratories to industrial products, faces a core challenge arising from the enormous material design space. The trial-and-error processes used in research laboratories is not suitable for these complex reactive systems, in which not only the chemistry (nature of fuel and oxides) but also the microscopic (size of the fuel and oxidizer particles, purity of metal) and mesoscopic properties (powder density, stoichiometric conditions, binder) in?uence the macroscopic combustion performance. Unfortunately, in spite of three decades of research in the ?eld of thermites, there is no truly predictive physical models able to provide reliable design guidelines to engineers and experimentalists, i.e able to predict the structure-property relationship and limit of design space. The reason of this is that the physics governing the thermites combustion in real-world situations, i.e. where combustion gases are mixed and interact with burning particles, is still poorly understood. Hence, the current modelling approaches su?er from several de?ciencies and over-simpli?cations that greatly degrades their accuracy : they do not consider the chemical and physical mechanisms at the microscale, i.e. at the scale of the particles experiencing chemical reactions, heat- mass- and momentum transfer, phase transition, and interactions between particles and with the gas which are all critical in the ?ame dynamics. The gas phase kinetics is also
too poorly described.

The project OASYS will provide a quantum leap in the theoretical description of the multiphase ?ow physics and chemistry of high temperature and fast propagating thermite reactions, and will permit fundamental changes to existing modelling methods – by developing the ?rst generation of multi-scale models describing the multiphase combustion process. It will also deliver the ?rst Computational Aided Engineering platform (CAE-tools) that will combine multiscale physical models in order to design an optimal Al-based thermite for a given device and application.

This ambitious goal raises a number of fundamental scienti?c issues and technical challenges that have never been addressed to date, which will constitute the scienti?c objectives of the project : (1) understanding in depth the multiphase ?ow physics of Al-based
thermite combustion, (2) developing a realistic description of the self-propagating combustion front in thermites.