Browsing by Author "Roberts, Andrew"

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    Ballistic impact of hollow-point ammunition on porcine bone
    (Wiley, 2023-05-06) Watson, Kayla E.; Henwood, Bailey; Hewins, Kate; Roberts, Andrew; Hazael, Rachael
    Identifying failure mechanisms in skeletal tissue allows a deeper understanding of the effects of specific projectile impacts on bone. While ballistic trauma in flat bones is largely researched, knowledge of how long bones react to gunshot impacts is limited in the literature. The impacts of deforming ammunition appear to produce higher levels of fragmentation; however, these have not been studied in depth. This study compares the damage to femora bone by HP 0.357 and 9 mm projectiles constructed with both full and semi-metal jackets. Impact experiments were undertaken on a single-stage light gas gun involving the use of a high-speed video camera and full reconstruction of the bones to ascertain fracture patterns occurring in the femora. Higher degrees of fragmentation are likened to the presence of semi-jacketed HP projectiles than jacketed HP projectiles. The observations of external facing beveled edges are believed to be associated with the increased separation of the jacket and lead core of projectiles. Additionally, experimentation has shown that the amount of kinetic energy lost postimpact is likely related to the presence or the absence of a metal jacket on an HP projectile. The observed data, therefore, suggest that the composition, rather than the configuration, of a projectile affects the type and extent of the damage.
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    Fragmentation studies by non-explosive cylinder expansion technique
    (Elsevier, 2020-09-04) Rao, Prakash; Painter, Jonathan; Appleby-Thomas, Gareth J.; Critchley, Richard; Wood, David; Roberts, Andrew; Hazael, Rachael
    Expansion and fragmentation of metallic cylinders is an important area of study both for designing munitions and mitigation techniques against fragments as well as in the failure of pressurised pipes in industry. Most of the reported studies on fragmentation have been carried out by detonating explosively filled metallic cylinders. However, this approach has inherent limitations in terms of both safety and repeatability – not least due to packing issues with explosive fills. Fragmentation studies on hollow metallic cylinders of both mild and stainless steel of various thicknesses (2–4 mm) were carried out by firing a polycarbonate projectile from a single-stage light gas gun. Strain rates of the order of 2 × 104 s−1 were observed at cylinder expansion velocities of 400–450 m s−1, calculated from flash X-ray radiographs. The differences in fragmentation behaviour of both materials was observed, attributed to their different response to high strain-rate loadings. Microscopic analysis of mild steel fragments showed interesting alignment of ferrite and pearlite grains, similar to reported effects of explosive loading. This suggests the potential to employ this technique to simulate explosive cylinder expansion in a non-explosive laboratory environment enabling a convenient recovery of fragments. Numerical modelling with using ANSYS AUTODYN® allowed for a better understanding of the various parameters controlling expansion and fragmentation. Analysis of recovered fragments by a Fragment Weight Distribution Map (FWDM), a method generally used for characterising pipe bombs, could clearly demonstrate the effect of casing material and thickness.
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    An investigation into the deceleration mechanisms of a projectile travelling through a liquid and the influence of hydrodynamic-ram effect
    (Straightline Publishing Limited, 2021-12-31) Blythe, D.; Evans, R.; Oldershaw, S.; Vann, C.; Miller, David; Easton, L.; Roberts, Andrew
    If fragmentation or a projectile such as a bullet were to penetrate an aluminium fuel tank, kinetic energy is introduced to the fluid contained within that tank. In turn, kinetic energy is also imparted to the aluminium tank structure, causing structural damage. This research project focussed on designing and constructing a re-usable vessel for repeat firing of projectiles into a liquid and the investigation of the hydrodynamic ram effect. The vessel should enable the use of high-speed imaging to allow the measurement and analysis of deceleration of different projectiles at different velocities.
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    The mechanical and optical response of Polychlorotrifluoroethylene to one-dimensional shock loading
    (Springer, 2015-07-24) Millett, Jeremy C. F.; Lowe, Michael R.; Appleby-Thomas, Gareth J.; Roberts, Andrew
    A series of plate impact experiments have been performed to probe the shock behavior of polychlorotrifluoroethylene (PCTFE), in terms of its optical and mechanical response. Interfacial velocity measurements using interferometric techniques have shown differences between measured and actual velocities, and been used to determine changes in refractive index due to shock-induced density increases. These have further been used to determine an optical correction factor, and allow the possibility of PCTFE being used as an optical window in future shock loading experiments. The shear strength of shock loaded PCTFE has also been shown to be near-constant behind the shock front, in common with other fluorinated polymers, although the strength variation with impact stress is greater than other similar materials. It has been suggested that the presence of a larger chlorine atom replacing a fluorine allows for a degree of tacticity between polymer chains, with local variations of charge density along the chain (due to the presence of the chlorine atom) also having an effect.
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    The Strength of two HMX based plastic bonded explosives during one dimensional shock loading
    (Springer, 2017-03) Millett, Jeremy C. F.; Taylor, P.; Roberts, Andrew; Appleby-Thomas, Gareth J.
    A series of experiments have been performed to probe the mechanical response of two HMX based plastic bonded explosives to one dimensional shock loading. Manganin stress gauges in longitudinal and lateral orientation to the loading axis have been used as the diagnostic. Results indicate that despite major differences in the binder phase and smaller differences in the HMX crystal loading and morphology, the Hugoniot and shear strengths behind the shock front are near identical. We have proposed that this is due to the HMX crystals forming a network that supports the bulk of the applied stress.
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    Surface damage in woven carbon composite panels under orthogonal and inclined high-velocity impacts
    (MDPI, 2022-09-26) Marchante Rodriguez, Veronica; Grasso, Marzio; Zhao, Yifan; Liu, Haochen; Deng, Kailun; Roberts, Andrew; Appleby-Thomas, Gareth J.
    The present research is aimed at the study of the failure analysis of composite panels impacted orthogonally at a high velocity and with an angle. Woven carbon-fibre panels with and without external Kevlar layers were impacted at different energy levels between 1.2 and 39.9 J. Sharp and smooth gravels with a mass from 3.1 to 6.7 g were used to investigate the effects of the mass and the contact area on the damage. Optical microscopy and thermography analyses were carried out to identify internal and surface damage. It was identified that sharp impactors created more damage on the impacted face of the panels, while the presence of a Kevlar layer increased the penetration limit and reduced the damage level in the panel at a higher energy.