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Loading and transient response of structures subjected to air-blast loading using Digital Image Correlation

   Department of Civil and Structural Engineering

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  Prof Genevieve Langdon  No more applications being accepted  Self-Funded PhD Students Only

About the Project

The loading generated on the surface of a structure following detonation of a near-field high explosive is extremely high in magnitude, short in duration, and is highly spatially non-uniform. These loads cause highly non-linear deformation and failure of structures such as plates and panels. The efficient design of blast protection systems is currently inhibited by an inability to accurately predict these nearfield blast loads and the subsequent structural response. There is dearth of well-controlled scientific data in the extreme near-field, which is in part due to the difficulties associated with direct measurement of blast loads and conflicting requirements for experimental techniques: robustness to survive 100s–1,000s MPa pressures and temporal sensitivity to sample pressures at MHz frequencies.

High speed video imaging techniques that can operate and record data in the vicinity of explosions offer the ability to determine the transient response and failure of such structures. Recent advancements in experimental capability at the University of Sheffield have enabled the measurement of both the loading acting on a rigid surface following detonation of a high explosive, and the response of a flexible target under the same blast load using Digital Image Correlation of high speed video footage. Preliminary studies have shown that the target initially begins to respond in a manner that is dictated by the specific impulse of the blast. That is, the initial velocity of the plate is directly proportional to specific impulse through conservation of momentum. This offers up an interesting series of challenges: can we measure the loading acting on a surface by quantifying the initial velocity with which it begins to respond? Can we calculate the transient response of a target, knowing its initial velocity distribution? Are there ways to rapidly assess the performance of a structure knowing its properties and the loading applied to it? For example, can assumed-modes analytical modelling techniques be adapted to predict the behaviour of plates subjected to measured initial velocity profiles?

Past work on measuring transient response to near field blast loads has examined the behaviour of steel alloys with significant plastic capacity. Materials with enhanced yield strengths (such as RHA steels) and/or limited ductility (such as fibre reinforced polymer composites) are likely to exhibit transient behaviour that differs greatly from the permanently deformed profile evident after an explosive event. This project would have the potential to study the response modes of such structures and materials, as well as more traditional steels studied extensively in the past.

The candidate should have background knowledge in practical studies and imaging techniques (high speed video), as well as a prior education and experience in structural mechanics/dynamics. You will be joining The Blast and Impact Research Group at The University of Sheffield, with 4 academic staff members, 3 postdoctoral researchers, and 13 PhD students. The Blast and Impact Research Group has decades of research experience into the mechanisms of loading arising from explosion events and their subsequent effects on structures and materials. Our goal is to determine the underlying mechanisms involved in the loading and responses arising from explosion and impact events with a view to improving the safety of people and infrastructure at risk. Our work balances fundamental scientific research and real-world impact, allowing us to play a key role in the development of new solutions to protect people and structures against the damaging effects of high explosive blasts.

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