The role of inter-particle shear in the shock-induced reaction of energetic materials
Supervisor: Dr Daniel Eakins
In heterogeneous energetic materials, shock waves can be used to bring separated reactants together and initiate chemistry over a broad range of timescales. For rapid initiation (under tens of nanoseconds), mass must be transported between reactants faster than can be accomplished by diffusion. Recent work on Ni+Al powders suggests an alternate mechanism that involves rapid mechanical deformation and interparticle shear. Extending these observations to other reactive systems however, is complicated by the numerous interface orientations and uncontrollable shear conditions in powder materials.
The Institute of Shock Physics is looking to start a PhD studentship to study shock-induced reactions along a well-defined interface between binary reactants. The student will explore the role of interface angle on shear flow and chemical reaction in intermetallic-forming systems, such as aluminides (Ni+Al, Ti+Al, etc.) or silicides (e.g., Ti+Si, Mo+Si), by performing shock compression experiments on binary reaction couples using the Institute's new 100mm bore gas-gun. Experiments will couple in situ measurements of stress and material velocity, with post-shock characterisation of recovered material. The experimental work will be augmented with numerical simulations, to estimate the mechanical state produced along the interface, and provide details of transient material flow. The student will be asked to explore the effect of interfacial shear on interface stability, mass mixing, and chemical reaction, and relate these observations to material properties such as density, yield strength, and melt temperature. As this understanding matures, focus will shift to ordered reactive materials, and study of cumulative flow along an ensemble of interfaces.
The understanding gained from this work will directly influence both predictive and design capabilities, with regard to the shock response of heterogeneous energetic and non-energetic materials. Knowledge of the role of interface configuration on initiation behaviour can help refine mesoscale models used to simulate the behaviour of existing composite energetics, and can be used to guide the microengineering of energetic materials to control the rate and extent of energy release.