Browsing by Author "Shackel, James"

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    A comparison of the ballistic behaviour of conventionally sintered and additively manufactured alumina
    (Elsevier, 2019-06-20) Appleby-Thomas, Gareth J.; Jaansalu, Kevin; Hameed, Amer; Painter, Jonathan; Shackel, James
    Production of ceramic armour solutions on-demand/in-theatre would have significant logistical and military advantages. However, even assuming that such technologies could be successfully deployed in the field, such near net-shape manufacturing technology is relatively immature compared to conventional sintering of ceramics. In this study, the ballistic performance of a series of additively manufactured (AM)/rapidly-prototyped (RP) alumina tiles of 97.2% of the density of Sintox FA™ were investigated using both forward- and reverse-ballistic experiments. These experiments, undertaken with compressed gas-guns, employed the depth-of-penetration technique and flash X-ray as primary diagnostics to interrogate both efficiency of penetration and projectile-target interaction, respectively. The RP alumina was found to exhibit useful ballistic properties, successfully defeating steel-cored (AP) 7.62 × 39 mm BXN rounds at velocities of up-to c.a. 850 m/s, while exhibiting comparable failure modes to conventionally sintered armour-grade Sintox FA™. However, where a <1% by vol. Cu dopant was introduced into the RP material failure modes changed dramatically with performance dropping below that of conventionally sintered alumina. Overall, the results from both sets of experiments were complimentary and clearly indicated the potential of such RP materials to play an active role in provision of real-world body armour solutions provided quality control of the RP material can be maintained.
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    An investigation into the variability of ABS 3D printing filaments due to differing dye colourants used by manufacturers
    (2019-12) Wright, Gary; Shackel, James; Errickson, David; Painter, Jonathan
    Despite advances in polymer filaments available for 3D printing, ABS remains an attractive polymer for use because of its versatility, good mechanical properties and cost effectiveness. Personal experience has highlighted variability between manufacturer’s ranges and even occasionally between the colours within those ranges. This variability seems to affect the quality of print and level of success achieved. In this study, analytical techniques, including X-ray diffraction (XRD), Dynamic Mechanical Analysis (DMA), Differential Scanning Calorimetry (DSC), RAMAN spectroscopy, and Fourier Transform Infra-Red (FTIR) spectroscopy, as well as mechanical tensile testing and Scanning Electron Microscopy (SEM) imaging, were used to compare and contrast selected colours from 3 different manufacturer’s ranges. This allowed comparison by chemical composition, physical properties such as glass transition temperature and by mechanical performance. Differences were found in their chemical composition, base polymer properties and their mechanical performance and some of this data did not match the information supplied by the manufacturers. A large analytical comparative study such as this lends itself to becoming quite complex, and this was reinforced by the practical difficulties encountered during the work which limited the conclusions that could be drawn. Significant variability was found between the manufacturer’s ranges themselves, and in some instances by colours within ranges. These differences were evident by way of DSC and DMA responses for glass transitions, compositions shown by FTIR and crystallinity from XRD, and occasionally also large statistically significant variability in mechanical tensile properties. Despite these findings, and practical experience implying otherwise, there was no conclusive link found that the variability of colour of the filament is responsible for the variability of print quality. Indeed, the variability between the base polymer i blends comparing each of the manufacturer’s ranges was found to be higher than that between the colours within the ranges themselves.
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    A novel hypothesis for the formation of conoidal projectile wounds in sandwich bones
    (Springer, 2018-10-18) Rickman, John M.; Shackel, James
    When perforated by a projectile, sandwich bones typically exhibit wounds with a distinct conoidal morphology that is widely utilised both in wound diagnosis and trajectory determinations. However, the dynamic fracture mechanisms underlying this intriguing wound type have yet to be experimentally verified. The most frequently quoted hypothesis for their formation, plug and spall, is difficult to reconcile with the conoidal morphology exhibited by such wounds. The present article carries out a high-speed videographic and micro-computerised tomographic (μ-CT) analysis of perpendicularly produced projectile wounds induced from 139.15 to 896.84 metres per second (m/s) in pig scapulae. Fundamental data on energy absorption, wound shape and bevel symmetry are presented. Cross-sectional fracture morphology revealed by μ-CT raises the novel hypothesis that tensile stresses induced by the projectile in the outer cortex elicit cone crack formation and that this cone crack then propagates catastrophically through the entire sandwich structure. This process results in the momentary formation of a bioceramic conoid, a conoidal volume of bone consisting of all three sandwich bone layers separated from the parent bone by the internal bevel. Fragmentation of the separated volume leaves the conoidal wound behind as its counterpart. The significance of this hypothesis in terms of differential diagnosis and interpretation of bevel shape is discussed.