Blastech Ltd

United Kingdom

Blastech Ltd

United Kingdom
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Barr A.D.,University of Sheffield | Clarke S.D.,University of Sheffield | Tyas A.,University of Sheffield | Tyas A.,Blastech Ltd | And 2 more authors.
Experimental Mechanics | Year: 2017

Split Hopkinson pressure bar experiments on soils are often carried out using a rigid steel confining ring to provide plane strain conditions, and measurements of the circumferential strain in the ring can be used to infer the radial stress on the surface of the specimen. Previous experiments have shown evidence of irregular electromagnetic interference in measurements of radial stress, which obscures the signals and impedes analysis. The development of robust constitutive models for soils in blast and impact events relies on the accurate characterisation of this behaviour, and so it is necessary to isolate and remove the source of interference. This paper uses an induction coil to identify the source of the anomalous signals, which are found to be due to induced currents in the gauge lead wires from the movement of magnetised pressure bars (martensitic stainless steel, 440C). Comparative experiments on sand and rubber specimens are used to show that the deforming soil specimen does not make a significant contribution to this activity, and recommendations are made on reducing electromagnetic interference to provide reliable radial stress measurements. © 2017, The Author(s).

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.

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.

Tyas A.,University of Sheffield | Tyas A.,Blastech Ltd. | Bennett T.,University of Sheffield | Warren J.A.,University of Sheffield | And 3 more authors.
Applied Mechanics and Materials | Year: 2011

The total impulse imparted to a target by an impinging blast wave is a key loading parameter for the design of blast-resistant structures and façades. Simple, semi-empirical approaches for the prediction of blast impulse on a structure are well established and are accurate in cases where the lateral dimensions of the structure are sufficiently large. However, if the lateral dimensions of the target are relatively small in comparison to the length of the incoming blast wave, air flow around the edges of the structure will lead to the propagation of rarefaction or clearing waves across the face of the target, resulting in a premature reduction of load and hence, a reduction in the total impulse imparted to the structure. This effect is well-known; semi-empirical models for the prediction of clearing exist, but several recent numerical and experimental studies have cast doubt on their accuracy and physical basis. In fact, this issue was addressed over half a century ago in a little known technical report at the Sandia Laboratory, USA. This paper presents the basis of this overlooked method along with predictions of the clearing effect. These predictions, which are very simple to incorporate in predictions of blast loading, have been carefully validated by the current authors, by experimental testing and numerical modelling. The paper presents a discussion of the limits of the method, concluding that it is accurate for relatively long stand-off blast loading events, and giving some indication of improvements that are necessary if the method is to be applicable to shorter stand-off cases. © (2011) Trans Tech Publications.

Clarke S.D.,University of Sheffield | Fay S.D.,University of Sheffield | Fay S.D.,Blastech Ltd | Warren J.A.,University of Sheffield | And 7 more authors.
International Journal of Impact Engineering | Year: 2015

The role of the geotechnical conditions on the impulse delivered by a shallow buried charge has received much attention in recent times. As the importance of the soil in these events has become better understood, the control over the geotechnical conditions has improved. While previous work has investigated directly the role of geotechnical conditions on the magnitude of the impulse from a buried charge, the current work aims to identify how these same conditions also affect the repeatability of testing using soils. In this paper the authors draw together their work to date for a wide range of different soil types and moisture contents to investigate the variation in output from nominally identical tests. The methodology for the preparation of soil beds and the measurement of impulse is described along with the measured variations in peak and residual deflections of a target plate fixed to the impulse measurement apparatus. © 2015 Elsevier Ltd.

Rigby S.E.,University of Sheffield | Tyas A.,University of Sheffield | Tyas A.,Blastech Ltd | Bennett T.,University of Sheffield | And 3 more authors.
Proceedings of the Institution of Civil Engineers: Engineering and Computational Mechanics | Year: 2013

Empirical prediction methods are often used in the early stages of design to quantify the blast load acting on a structure. While these methods are reasonably accurate for geometrically simple scenarios, they may not be accurate for situations where the target does not form a reflecting surface of effectively infinite lateral extent. In this case, the blast wave will diffract around the target edge, leading to the propagation of a relief wave inwards from the edge of the structure, reducing the late-time development of pressure in a process known as 'clearing'. This paper presents results from a study undertaken to determine the influence of clearing on the response of simple targets. Experiments were conducted in which deflection-time histories were recorded for target plates subjected to cleared and non-cleared blast loads. These were compared with predictions from explicit dynamic finite-element and single-degree-of-freedom models, in which the blast loading was derived by applying a simple correction to the empirical blast prediction method. The results presented show that neglecting clearing may result in highly conservative predictions of target response and that analyses using loading derived from simple corrections to the ConWep predictions match the experimentally observed results very closely.

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.

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.

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.

PubMed | University of Sheffield, Blastech Ltd. and UK Defence Science and Technology Laboratory
Type: | Journal: Journal of visualized experiments : JoVE | Year: 2016

Near-field blast load measurement presents an issue to many sensor types as they must endure very aggressive environments and be able to measure pressures up to many hundreds of megapascals. In this respect the simplicity of the Hopkinson pressure bar has a major advantage in that while the measurement end of the Hopkinson bar can endure and be exposed to harsh conditions, the strain gauge mounted to the bar can be affixed some distance away. This allows protective housings to be utilized which protect the strain gauge but do not interfere with the measurement acquisition. The use of an array of pressure bars allows the pressure-time histories at discrete known points to be measured. This article also describes the interpolation routine used to derive pressure-time histories at un-instrumented locations on the plane of interest. Currently the technique has been used to measure loading from high explosives in free air and buried shallowly in various soils.

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