Browsing by Author "Stennett, Christopher"
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Item Open Access Chemical modification of β-cyclodextrins: balancing soft and rigid domains in complex structures(Wiley, 2019-09-19) Luppi, Federico; Mai, Nathalie; Kister, Guillaume; Gill, Philip P.; Gaulter, Sally; Stennett, Christopher; Dossi, EleftheriaCrystalline polymers such as β‐cyclodextrin (βCD) can be modified with polyethylene glycol (PEG) diglycidyl ether cross‐linkers (262, 394, 500 Da). Here we show that the quantity and length of the PEG soft segments influence the solubility and malleability of the products, which are water‐soluble and easily converted to nitrated analogues under standard reaction conditions. Inert and nitrated derivatives containing longer PEG segments showed the ability to self‐heal. The degree of cross‐linking and decomposition temperatures and energies depended on the quantity and length of the soft segment. Nitrated cross‐linked βCD containing longer PEG segments did not ignite following an electrostatic discharge of 4.5 J. The chemical stability of βCD/PEG binders was tested by heat flow calorimetry at 80 °C. We found that the balanced incorporation of soft PEG and rigid βCD segments improved the processability of cross‐linked βCDs and desensitised their nitrated derivatives, offering new solutions for inert and energetic binders.Item Open Access Enhancement of laser ignitibility of insensitive energetic materials (FOX-7)(Wiley, 2023-09-15) Stennett, Christopher; Gaulter, SallyExperimental investigation into the feasibility of optically sensitising an insensitive explosive, FOX-7 (1,1-Diamino-2,2-dinitroethene) by the doping of gold nanoparticles (GNPs) has been conducted. The commercially available GNPs were specifically designed in their particle shape and size to strongly absorb at the wavelength of the igniting laser (808 nm). The laser ignitibility of FOX-7 was significantly increased as the GNPs efficiently converted the absorbed energy into the heat. The laser ignitibility of such optically sensitised FOX-7 and the detonation capability of the laser initiator devices designed for the study were evaluated. Based on the evaluation of the initiator’s output in term of impact pressure, it was shown that an GNPs doped FOX-7 based laser slapper initiator was able to detonate a secondary explosive.Item Open Access Experimental fragmentation of pipe bombs with varying case thickness(Elsevier, 2019-11-05) da Silva, Luciana A.; Johnson, Steve; Critchley, Richard; Clements, Jim; Norris, Karl; Stennett, ChristopherAmong all the improvised explosive devices (IEDs) known, pipe bombs are one of the most popular devices used by terrorists. They are simple to use, easy to construct and materials are readily available. For this IED, fragmentation is the primary injury mechanism, which makes them a desirable weapon for terrorists aiming to inflict maximum human casualties. Although the investigation of fragmentation pattern is not novel, there is limited data available on pipe bombs performance in the open literature. Therefore, this research is looking at validating results in current literature, which showed limited repetition and weak experimental design so far; by trial with six pipe bombs with two different thickness (3 of each). The pipe bombs consisted of mild steel casing and aluminised ammonium nitrate as the explosive filler. Fragments were collected, with an average recovery of 72%, and measured regarding mass and velocity. The experiment results show a correlation between the pipe thickness and both the size and velocity of fragments.Item Open Access Gas gun ramp loading of Kel-F 81 targets using a ceramic graded areal density flyer system(Elsevier, 2015-03-06) Goff, Michael J.; Hazell, Paul J.; Appleby-Thomas, Gareth J.; Wood, David C.; Stennett, ChristopherKel-F 81 (PCTFE/Polychlorotrifluoroethylene) polymer targets were subjected to ramp loadings generated by a ceramic flyer accelerated into the targets by a gas gun in the plate impact configuration. This approach used a ceramic graded areal density flyer in conjunction with a ceramic buffer plate to induce a ramp loading in the target. The flyer was comprised of a rapid prototyped alumina ceramic. The loading was observed with embedded electromagnetic particle velocity gauges (PV gauges) with the results compared with ANSYS Autodyn™ hydrocode simulations. Experimental results show that ramp loadings of varying duration and magnitude were induced into the target. These loadings can be described as shockless compressions leading to shocked states within the material. In addition, numerical simulations provided further insight into the loading approach – with good agreement found with experimental data, opening the potential to design more complex loading systems in future.Item Open Access The Ignition Behaviour of Energetic Materials Under Confined Cookoff(2018-09) Stennett, Christopher; Akhavan, JacquelineIn a series of experiments and theoretical work, the process of ignition in confined energetic materials has been explored and understanding gained. Early work focused on the direct observation of the cook-off process but was hampered by the available technology. In more recent work, dynamic measurements of the deformation of the confinement have been explored, and refinements to the direct observation method have been made that make use of recent advances in camera technology. We have observed, for the first time, complex melting and development of gas spaces within which the early stages of ignition take place, and propose a new mechanism by which violent cook-off responses might develop in certain explosivesItem Open Access Optical sensitisation of energetic crystals with gold nanoparticles for laser ignition(Elsevier, 2017-05-18) Fang, Xiao; Sharma, Mishminder; Stennett, Christopher; Gill, Philip P.The laser ignition of explosives is safer and more environmentally beneficial than electric ignition systems, but optical sensitisers must be present to facilitate heating by optical absorption. We investigated, for the first time, the optical sensitisation of cyclotrimethylenetrinitramine (RDX) crystals by doping them with gold nanoparticles to enhance laser ignitibility using a near-infrared diode laser. RDX crystals physically coated with gold nanoparticles or recrystallised from a solution containing gold nanoparticles were tested for optical sensitisation by micro-imaging with a scanning electron microscope, and high-speed video was used to experimentally observe the enhanced laser ignitibility. The gold nanoparticles achieved effective optical sensitisation and significantly enhanced the laser ignitibility of RDX, reducing the laser ignition threshold power from more than 45 W to as little as 1 W. Our results show that gold nanoparticles are effective as optical sensitisers for the ignition of energetic materials using a small, low-power diode laser.Item Open Access Printing powerful powders: evaluating static and dynamic behaviour(Cranfield University Defence and Security, 2024-11-13) Zyga, Jowita; McGee, Christine; Humphreys, Lisa; Stennett, ChristopherAdditive Manufacturing (AM), commonly referred to as 3D printing, is a promising manufacturing technique, enabling near full control of the final product’s properties. With its unique approach to complex objects manufacturing, AM is investigated for its suitability of manufacturing with a wider range of materials. Despite the global research on AM of Energetic Materials that has already been conducted, final energetic devices often offer poorer product performance, compared to traditional manufacturing techniques. Reasoning for poorer outcomes could be attributed to the need for adapting and modifying Energetic Materials for AM purposes. To make the materials suitable for AM, there is a need for material modification, such as mixing energetic ingredient with solvent or binder, both of which often result in reducing the desirable outcome: the use of solvent can lead to uneven drying and shrinkage (and therefore producing voids within the product); too much binder is often responsible for low energetic density, therefore causing high burn rates and detonation velocities to be inaccessible. To overcome that, it would be beneficial to use raw, unmodified Energetic Materials – in their powdered form. Research conducted at Cranfield University, using Dry Powder Additive Manufacturing has proven, that energetic devices can be successfully printed using energetic powders. However, working with powders is often challenging: a lack of continuous flow, powder caking or powder-dispensing nozzle blockages are often experienced. To maximise the final product performance and avoid above issues, it is necessary to understand powder behaviour: its dynamic flow, bulk, shear and process properties. A deep understanding of those properties and their effect on manufacturing process is a crucial step to further developing this AM technique. Current methods of powder characterisation are typically limited to determination of 3 parameters: Angle of Repose, Carr (Compressibility) Index and Hausner Ratio. Scientific community have, however, proven these methods to be unreliable, proposing more thorough ways of powder studies: powder rheometers. Despite their growing popularity, analysis and interpretation of test results can still pose some challenges. Current research focuses on gaining better understanding of powder rheology and recognising how investigated powders’ properties translate to their behaviour during the printing process.Item Open Access Pulsed laser irradiation of a nanoparticles sensitised RDX crystal(Elsevier, 2020-01-30) Xiao, Fang; Stone, Matthew; Stennett, ChristopherThe laser initiation of secondary explosives presents tactical, safety and environmental advantages over traditional ignition systems utilising primary explosives. In this paper, direct ignition or initiation by pulsed laser was investigated of cyclotrimethylenetrinitramine (RDX) crystals doped with gold nanoparticles (GNPs) for the first time. A nano-seconds pulsed laser was used for direct irradiation of the crystals at the GNP's surface-plasmon-resonance wavelength of 532 nm. RDX crystals were recrystallised from a solution containing GNPs and characterised by visual microscopy for surface coating and subsurface doping. A high-speed camera was used to observe and capture the modes of interaction between the GNPs-doped RDX crystals and pulsed laser irradiation with a new classification method. Laser fluence thresholds for ignition and initiation were established. The GNPs sensitized RDX to pulsed laser irradiation at this selected wavelength is 3 orders of magnitude more sensitive than pure RDX. Direct initiation of the GNPs doped RDX crystal at laser fluence of 0.04 J/cm2 led to the total consumption of a crystal sample, which was unreproducible with pure RDX. The results show that GNPs are effective optical sensitizers for direct initiation of RDX crystal by low-power pulsed laser.Item Open Access Small-scale characterisation of urea hydrogen peroxide explosive performance using heterodyne velocimetry(Royal Society of Chemistry, 2022-06-24) Halleux, Francis; Stennett, Christopher; Pons, Jean-François; Wilson, Ian; Lefebvre, MichelUrea Hydrogen Peroxide (UHP) is widely available in the cosmetic and pharmaceutical industries. UHP exhibits the behaviour of a tertiary explosive and previous research from the same authors has highlighted its detonability at small-scale under heavy confinement. In this work, UHP performance parameters are further investigated by heterodyne velocimetry. An average detonation pressure of 3.7 GPa for UHP at a mean density of 0.75 g/cm3 has been determined using the impedance window method, corresponding to a 20% TNT equivalence for brisance. This result is consistent with calculation from empirical correlations. An average 3200 m/s detonation velocity was recorded using contact probes, in excellent agreement with measurements from passive optical probes. This small-scale experimental campaign, which was complementary to and consistent with previous research, has proven useful to characterise the performances of non-ideal explosives for risk assessment purposes.Item Open Access Towards understanding the detonation properties of additively manufactured RDX: Dry powder printed(Royal Society of Chemistry, 2022-06-22) McGee, Christine; Stennett, Christopher; Clements, Jim; Vrcelj, RankoResearch into additive manufacturing (AM) has been steadily expanding over the past five decades. Where once only polymeric materials could be reliably printed, AM has been adapted to print with a range of materials such as biological, metallic, ceramic and even foodstuffs. The advantages of manufacturing in an additive manner include; a) a layer-by-layer approach allows the creation of architecturally complex structures, b) a reduction in weight, c) lessening of waste and d) the ability to create parts that that are otherwise difficult or too costly to produce. 1,3,5-Trinitro-1,3,5-triazinane (RDX) is regularly used in explosive systems. Its detonation properties when conventionally manufactured are widely researched and broadly understood. However, recent advances in additive manufacturing technologies have led to greater interest in utilising RDX in this manner. There is growing evidence that emerging formulations and printing methods are changing the detonation properties of RDX composites, the critical diameter among them.1 This study reports on beginning to understand the detonation properties of additively manufactured RDX via a dry powder printing method.Item Open Access Urea-Hydrogen Peroxide (UHP): comparative study on the experimental detonation pressure of a non-ideal explosive(Wiley, 2023-08-28) Halleux, Francis; Pons, Jean-François; Wilson, Ian; Stennett, Christopher; Van Riet, Romuald; Lefebvre, MichelCarbamide Peroxide, an adduct of Urea and Hydrogen Peroxide (UHP) industrially used as a solid source of hydrogen peroxide, exhibits the behaviour of a tertiary explosive but a detailed performance characterisation is still lacking in the literature. In this work, we calculated a 20% experimental TNT equivalence for brisance, i.e. the shattering effect from the shock wave transmitted from the detonating high explosive into adjacent materials, by experimental indirect measurement of UHP detonation pressure. We determined a 3.5 GPa detonation pressure for 5 kg unconfined UHP charges (0.87 g/cm3, 120 mm charge diameter) by measuring the attenuated shock wave velocity (ASV) in adjacent inert materials using passive optical probes. Particle velocity measurements at the interface of a PMMA impedance window carried out with Photonic Doppler Velocimetry on scaled-down charges of 90 g UHP under heavy confinement (0.85 g/cm3, 30 mm charge diameter, 4 mm thick steel) are consistent with ASV results in the PMMA acceptors but further investigations are required to determine the detonation pressure, using a small-scale experimental set-up. The ASV method has proven reliable to assess the brisance of a non-ideal explosive for risk assessment purposes.