Browsing by Author "Gaulter, Sally"

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    Andrew Claydon PhD
    (Cranfield University, 2020-11-27 10:15) Gill, Philip; Claydon, Andrew; Gaulter, Sally; Kister, Guillaume
    Current Polymer Bonded Explosive (PBX) formulation is limited by a compromise - optimised final properties against processability. While explosive content would ideally be maximised and plasticiser content ideally minimised, the formulation would become too viscous to cast and require arduous mixing processes using conventional techniques. However, with Resonant Acoustic Mixing (RAM), formulation does not have to be constrained. Instead of mixing blades, mixing is achieved using an oscillating platform to impart acoustic pressure waves (vibrations) into the mixture. Mixing is orders of magnitude faster than conventionally achievable, and the added ability to mix in the end use casing (mixing ‘in-situ’) also renders casting obsolete in many scenarios. The research aim of the PhD is to assess how machine control and vessel design can be altered to optimise the mixing mechanism and compare material properties of composites mixed ‘in-situ’ and ‘mixed and cast’.
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    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, Eleftheria
    Crystalline 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.
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    Determination and optimisation of Resonant Acoustic Mixing (RAM) efficiency in Polymer Bonded eXplosive (PBX) processing
    (Elsevier, 2022-02-07) Claydon, Andrew J.; Patil, Ajay N.; Gaulter, Sally; Kister, Guillaume; Gill, Philip P.
    An investigation into how the efficiency (time and energy required for homogeneity) of Resonant Acoustic Mixing (RAM) can be determined and optimised was undertaken. An idealised Polymer Bonded eXplosive (PBX) simulant based on glass microbeads (28.3 um D50, 62% v/v in binder and plasticiser) was used for mixing. Mixing evolution was monitored using machine output data, whereby the mixer ‘intensity’ (related to power draw) was plotted against time. Experiments were undertaken with three acceleration settings, three mixer units, and three vessel materials of low, medium, and high surface free energy. Different stages of the mixer ‘intensity’ profiles were found to correspond to discrete stages of mixing, as well as further rheological changes due to continued frictional heating, thus viscosity reduction, beyond homogeneity being achieved. Time to mixing completion was found to be repeatable within a standard deviation of +/- 10%, strongly dependent on acceleration setting, and additionally dependent on vessel material, though additional data is required to confirm this. A significant difference in mixing time was observed between different LabRAM units. Partial vacuum application without degassing was beneficial for mixing. Finally, a paradigm linking the ‘movement modes’ of mixing was constructed, based on literature observations and the experimental results.
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    Enhancement of laser ignitibility of insensitive energetic materials (FOX-7)
    (Wiley, 2023-09-15) Stennett, Christopher; Gaulter, Sally
    Experimental 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.
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    An estimate of the TNT-equivalent net explosive quantity (NEQ) of the Beirut port explosion using publicly-available tools and data
    (Wiley, 2020-10-21) Stennett, Chris; Gaulter, Sally; Akhavan, Jacqueline
    Publicly available video recordings of the explosion in Beirut on August 4, 2020, were examined and from them it was possible, in conjunction with the well‐known Google Maps website, to obtain estimates for the locations of the observers’ cameras with respect to the blast, and estimates for the blast wave arrival time. A publicly‐available blast wave calculator was then used to estimate the size of the explosion in terms of the equivalent quantity of TNT that would produce the same blast wave arrival time at the observers’ distance. This work estimates the Beirut explosion to have been equivalent to 637 tons TNT, with a lower bound estimate of 407 tons and an upper bound estimate of 936 tons
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    Resonant acoustic mixing of polymer bonded explosives
    (2021-01) Claydon, Andrew J.; Gill, Philip P.; Kister, Guillaume; Gaulter, Sally; Flood, Nathan
    Current Polymer Bonded Explosive (PBX) formulation is limited by a compromise - optimised final properties against processability. While solid loading (explosive content) would ideally be maximised and plasticiser content would ideally be minimised, this would make the formulation too viscous to cast into its casing and require long and arduous mixing processes using conventional techniques. However, with Resonant Acoustic Mixing (RAM), PBX formulation does not have to be constrained. Instead of traditional mixing blades, mixing is achieved by the use of a vibrating platform to impart acoustic pressure waves (vibrations) into the mixture, agitating it. The added ability to mix in the end use casing (mixing ‘in-situ’) also renders casting obsolete in many scenarios. In order to maximise the benefits of RAM with regards to next generation formulation-optimised PBX manufacture (‘PBneXt’), the underlying mechanisms of how the technique works, how efficiency (time and energy required for homogeneity) can be determined and maximised, and how final material properties may change between casting and ‘in-situ’ processing methods, must be better understood. The research aim of the PhD is therefore to assess how mixing efficiency of RAM can be measured and optimised to maximise its benefits, with a focus on how aspects of machine control and mixing vessel design can be altered to improve the mixing mechanisms on which the technique relies. Areas investigated experimentally include the effects of acceleration and mixer intensity (linked to power draw) setting, mixer model and unit, vessel material (with regards to surface free energy and thermal properties), and vessel surface finish (with regards to roughness). It is found that by modifying these variables, the time and energy required for mixing can be substantially reduced. A comparison between material properties of composites mixed ‘in-situ’ and ‘mixed and cast’ is also undertaken. The findings are then reconciled with wider literature observations and recommendations are made as how to best implement RAM for ‘PBneXt’ manufacture, ultimately allowing for explosive compositions with improved performance, mechanical, safety, and ageing properties.