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Tyas A.,University of Sheffield | Warren J.A.,University of Sheffield | Bennett T.,University of Sheffield | Fay S.,Blastech Ltd
Shock Waves | Year: 2011

It is well known that when a blast wave strikes the face of a target, the duration of the loading, and hence the total impulse imparted to the target may be influenced by the propagation of a rarefaction, or "clearing" wave along the loaded face of the target adjacent to free edges. Simple methods of predicting the effect of clearing on reducing the blast loading impulse have been available for many years, but recent studies have questioned the accuracy and physical basis of these approaches. Consequently, several authors have used numerical modelling and/or experimental techniques to determine empirical predictive methods for the clearing effect. In fact, the problem had been addressed more than 50 years ago in a study which appears to have been since overlooked by the blast research fraternity. This article presents the results of that earlier study, and provides experimental validation. The analytical predictions are very simple to determine, and are shown to be in excellent agreement with experimental results. © 2011 Springer-Verlag. Source

Ozdemir Z.,University of Sheffield | Hernandez-Nava E.,University of Sheffield | Tyas A.,University of Sheffield | Warren J.A.,University of Sheffield | And 4 more authors.
International Journal of Impact Engineering | Year: 2016

Lattice structures offer the potential to relatively easily engineer specific (meso-scale properties (cell level)), to produce desirable macro-scale material properties for a wide variety of engineering applications including wave filters, blast and impact protection systems, thermal insulation, structural aircraft and vehicle components, and body implants. The work presented here focuses on characterising the quasi-static and, in particular, the dynamic load-deformation behaviour of lattice samples. First, cubic, diamond and re-entrant cube lattice structures were tested under quasi-static conditions to investigate failure process and stress-strain response of such materials. Following the quasi-static tests, Hopkinson pressure bar (HPB) tests were carried out to evaluate the impact response of these materials under high deformation rates. The HPB tests show that the lattice structures are able to spread impact loading in time and to reduce the peak impact stress. A significant rate dependency of load-deformation characteristics was identified. This is believed to be the first published results of experimental load-deformation studies of additively manufactured lattice structures. The cubic and diamond lattices are, by a small margin, the most effective of those lattices investigated to achieve this. © 2015 Elsevier Ltd. Source

Rigby S.E.,University of Sheffield | Tyas A.,University of Sheffield | Tyas A.,Blastech Ltd | Bennett T.,University of Adelaide | And 3 more authors.
International Journal of Protective Structures | Year: 2014

Following the positive phase of a blast comes a period where the pressure falls below atmospheric pressure known as the negative phase. Whilst the positive phase of the blast is well understood, validation of the negative phase is rare in the literature, and as such it is often incorrectly treated or neglected altogether. Herein, existing methods of approximating the negative phase are summarised and recommendations of which form to use are made based on experimental validation. Also, through numerical simulations, the impact of incorrectly modelling the negative phase has been shown and its implications discussed. Source

Warren J.,Blastech Ltd | Kerr S.,UK Defence Science and Technology Laboratory | Tyas A.,University of Sheffield | Clarke S.,University of Sheffield | And 4 more authors.
Proceedings of the Institution of Civil Engineers: Engineering and Computational Mechanics | Year: 2013

The Defence Science and Technology Laboratory sponsored, QinetiQ-led Force Protection Engineering Research Programme has two main strands, applied and underpinning research. The underpinning strand is led by Blastech Ltd. One focus of this research is into the response of geomaterials to threat loading. The programme on locally won fill is split into four main characterisation strands: high-stress (GPa) static pressure-volume; medium-rate pressure- volume (split Hopkinson bar); high-rate (flyer plate) pressure-volume; and unifying modelling research at the University of Sheffield, which has focused on developing a high-quality dataset for locally won fill in low and medium strain rates. With the test apparatus at Sheffield well-controlled tests can be conducted at both high strain rate and pseudo-static rates up to stress levels of 1 GPa. The University of Cambridge has focused on using onedimensional shock experiments to examine high-rate pressure-volume relationships. Both establishments are examining the effect of moisture content and starting density on emergent rate effects. Blastech Ltd has been undertaking carefully controlled fragment impact experiments, within the dataspace developed by the Universities of Sheffield and Cambridge. The data from experiments are unified by the QinetiQ-led modelling team, to predict material behaviour and to derive a scalable locally won fill model for use in any situation. Source

Clarke S.D.,Sir Frederick Mappin Building | Fay S.D.,Sir Frederick Mappin Building | Fay S.D.,Blastech Ltd | Warren J.A.,Sir Frederick Mappin Building | And 4 more authors.
Measurement Science and Technology | Year: 2015

A large scale experimental approach to the direct measurement of the spatial and temporal variation in loading resulting from an explosive event has been developed. The approach utilises a fixed target plate through which Hopkinson pressure bars are inserted. This technique allows the pressure-time histories for an array of bars to be generated, giving data over a large area of interest. A numerical interpolation technique has also been developed to allow for the full pressure-time history for any point on the target plate to be estimated and hence total imparted impulse to be calculated. The principles underlying the design of the experimental equipment are discussed, along with the importance of carefully controlling the explosive preparation, and the method and location of the detonation initiation. Initial results showing the key features of the loading recorded and the consistency attainable by this method are presented along with the data interpolation routines used to estimate the loading on the entire face. © 2015 IOP Publishing Ltd. Source

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