Mechanisms and Characterisation of Explosions (MaCE)

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Analysis of the effects of high explosive blast loading on structures has applications in transport security, infrastructure assessment and defence protection. Engineers must utilise materials in efficient and effective ways to mitigate loads of extreme magnitudes, acting over milliseconds. But there is a fundamental problem which hampers research and practice in this field; we still do not fully understand the loads generated by a high explosive blast.Scientific characterisation of blast loading was a pressing issue in the middle of the last century, as researchers developed methods to predict the loading from large conventional blasts, and from atomic weapons at relatively long distances from targets. The huge amount of effort expended on this work, and the involvement of some of the world's leading physicists and mathematicians (G.I. Taylor, John von Neumann) reflected the existential nature of that threat. This work was predominately based on studying blast loading on targets at relatively long distances from detonations (far-field). Over the past few decades, whilst great advances have been made in understanding and designing materials to withstand extraordinary loads, experimental characterisation of blast loading itself has not kept pace in three key areas, which this project directly aims to address:Firstly, we don't know the magnitudes of explosive loading on targets very close to a high explosive detonation. Today's terrorist threats are frequently from smaller, focused, close-range explosions. Scenarios such as bombs smuggled onto aircraft, or targeted attacks on key items of critical infrastructure are ones in which such "near-field" loading is potentially devastating. But there is an almost total absence of high quality experimental work on characterising near-field blast loading. Predictions in these safety-critical areas currently rely on extrapolation of simple far-field models, or the use of inadequately validated numerical models. The project will provide new, properly validated, numerical models based on high quality experimental work to address this.This raises the second knowledge gap. Our current models of detonation-to-blast-wave mechanisms are based on simplified assumptions, such as that energy is released essentially instantaneously on detonation. Whilst this appears to work well for the far-field, there are major doubts over its validity in the near-field. This project will bring together blast engineers, high-temperature experimentalists, and energetic chemistry researchers to identify the role of early-stage post-detonation chemical reactions between the explosive fireball and the atmospheric oxygen in releasing energy, and how that affects the subsequent blast loading. The data gathered in the project will allow a new conceptual blast model to be created based on novel experimental analysis. The final knowledge gap is the question of whether blast loading in well-controlled scientific experiments is essentially deterministic or chaotic in nature. Addressing this issue is vital if the blast loading research community is to have the equivalent of a standard wind tunnel or shaking table test. Our preliminary work has led to the hypothesis that there is a region at the boundary between the near- and far-fields, where instabilities in the fireball will lead to large and random spatial and temporal variations in pressure loading, but that either side of this, the loading should be deterministic and determinable. The project will provide the data to validate this hypothesis, thus being able to provide guidance to other researchers in the field.Addressing these gaps, through a programme of multi-disciplinary experimental research, will produce a step change in our understanding of blast loading and our ability to protect against blast threats.