Browsing by Author "Stennett, C."

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    The effect of ionising radiation on the explosives: TATB, HMX and PETN
    (Cranfield University, 2019) Lewis, D. A.; Akhavan, Jacqueline; Cook, M.; Wilson, I; Stennett, C.
    The effect ionizing radiation, specifically gamma, has on three of the most well known explosive materials; HMX, PETN and TATB, has been studied experimentally and computationally. Samples of these explosives that had been irradiated in vacuum to a total dose (equivalent to water) of 200 kGy by an average incident energy of 1.25 MeV, showed changes to their explosive and physical properties to varying degrees, with sensitivity to impact being most notably changed for PETN and HMX. Changes to the thermal properties of HMX and TATB, alongside the detection of long lived radicals for TATB and PETN, suggests alterations to each material’s chemistry. Changes were only detectable in solid state analytical methods, indicating that alterations to these materials are isolated within this state. Through comparison with other data, these changes appear to be highly dependant on the gaseous environment in which they are irradiated, with vacuum having the most significant effect. The widely reported greening of TATB under the influence of gamma (and ultraviolet and x-Ray) irradiation was found to be reversible upon re-crystallisation, with the process also appearing to remove the long lived radical that had existed in the material for over eight years. Radical concentration appears to correlate with total absorbed dose along with the level of green within the material. Computational investigation attributes the discolouration of TATB to the cationic radical derivative of TATB, which is stabilised by de-localised pi-bonding resonance of the constitutive aromatic ring, it is also suggested that this is the source of the radical signal observed in ESR analysis.Further computational investigation suggests that purported decomposition products of TATB such as the mono-furazan, mono-nitroso and phenoxyl radical are not the source of the discolouration and are also not thermodynamically favourable, unless the monofurazan or phenoxyl derivatives are in a cationic form. Thermodynamic evaluation of potential decomposition pathways for PETN and HMX yield a selection of energetically favourable products, however the significant majority are, like TATB, in the cationic radical form. Simulated ESR spectra for purported HMX decomposition products did not agree with those observed in literature, attributed to their short lived nature. However a measured long lived radical in TATB is attributed to the cationic radical form of TATB, the purported source of the discolouration. A long lived radical in PETN was also measured and assigned to the cation derivative of PETN by comparison with computational predictions.
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    The effect of specimen thickness on the shock propagation along the in-fibre direction of an aerospace-grade CFRP laminate
    (Elsevier, 2009-02) Hazell, Paul J.; Stennett, C.; Cooper, G.
    In-fibre measurements of the Hugoniot have been carried out on a carbon fibre-reinforced polymer composite. For this material, we have shown at high shock stresses, a two component wave was formed consisting of a fast moving ramped portion and a slower moving shock wave. Changing the thickness of test specimen for a given shock stress resulted in a change in the magnitude and duration of the ramped portion of the wave front. As the shock stress imparted to the target was reduced, or the thickness of the target was increased, the steep shock wave in the rear surface gauge was no longer apparent. Instead a relatively slow rising wave was measured. Consequently, to establish a Hugoniot at lower shock stress levels, relatively thin specimens of target material are required.
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    A review of the mallet impact test for small scale explosive formulations
    (2016-07-01) Weaver, M.; Blair, L. H.; Flood, N.; Stennett, C.
    Development of new explosive formulations begins with the generation of only a few milligrams of material which is investigated using a number of small scale tests such as DSC, TGA, response to flame, mallet impact (mallet friction either glancing or direct blow) to determine whether the formulation is safe to scale up to 10 g. The latter of these tests, mallet impact, can be particularly subjective as the result is directly influenced by the operator carrying out the assessment. Not only can there be a change from one operator to another but there can also be a change in the force applied during each strike potentially leading to inconsistent results. This study highlights this encountered variation and assesses the load applied by a variety of operators with varying levels of explosive experience. This paper also proposes the use of a small scale laboratory based impact test which would provide improved confidence in the assessment of impact sensitiveness of explosive formulations and assist in justifying whether a formulation can be taken to the next scale. A small scale version of the BAM impact test (EMTAP Test 43) has been devised that allows the comparison of the sensitiveness of small scale formulations relative to RDX (8.7 J, EMTAP Test 43B) whilst also ensuring a reproducible result.
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    The shock and release behavior of an aerospace-grade cured aromatic amine epoxy resin
    (Wiley, 2008-06-20T00:00:00Z) Hazell, Paul J.; Stennett, C.; Cooper, G.
    Knowing the dynamic behavior of polymer materials that are used in the construction of fiber-reinforced composite materials is particularly important for such materials that are subjected to impact. In this work, we have conducted a number of plate-impact experiments on a commercially important aromatic amine epoxy resin that is used in the construction of carbon fiber composite materials. The measured Hugoniot in shock velocity–particle velocity space was Us = 2.65 + 1.55 up ( ρ0 = 1.141 g/cc), and is similar to the measured Hugoniots of other resins presented by different researchers. We have also measured the longitudinal stress in the shocked material and shown, in common with other polymers, that above a threshold stress, an increase in shear strength with impact stress is observ
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    The variation in lateral and longitudinal stress gauge response within an RTM 6 epoxy resin under one-dimensional shock loading
    (Springer , 2009-12-31T00:00:00Z) Appleby-Thomas, Gareth J.; Hazell, Paul J.; Stennett, C.
    The dynamic response of a commercially important epoxy resin (RTM 6) has been studied using plate impact experiments in the impact velocity regime of 80–960 m/s. Both longitudinal and lateral manganin stress gauges were employed to study the development of orthogonal components of stress both during and after shock arrival. In light of recent work raising doubts about the interpretation of lateral gauge data, lateral response within the RTM 6 resin was also used to investigate the physical phenomena being measured by the embedded lateral gauges. US–uP and rX–uP Hugoniot relationships were in good agreement with data for similar polymer materials from the literature. Derivation of shear strength behaviour both during and after shock arrival showed evidence of strengthening behind the shock front, attributed to compression of the cross-linked epoxy resin polymer chains. Comparison of the change in lateral stress behind the shock to the behaviour of an epoxy resin possessing a similar US–uP Hugoniot from the literature showed a different response; likely attributable to enhanced cross-linking present in this second resin. This result suggests that the embedded lateral gauges were, at least in part, measuring a physical response behind the shock within the resin. A Hugoniot elastic limit of 0.88 ± 0.04 GPa was derived and found to be of the same order of magnitude as results found elsewhere for similar materials.