Browsing by Author "Kister, G."
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Item Open Access Evaluation of novel propellants manufactured from commercially available Thermoplastic Elastomers (TPE) using resonant acoustic mixing(2019-06) Wilkinson, Peter John; Gill, Philip P.; Kister, G.The key issues in developing a sustainable gun or rocket propellants are financial, environmental, legislative and safety. Use of commercially available off the shelf polymers, in particular, thermoplastic elastomers (TPE) as a binder for propellants could address these issues. The propellant would need to have suitable mechanical and thermal properties, as well as, adequate ballistic performance. Traditional manufacture techniques for propellant are not suitable for TPE binders and so new mixing and manufacturing techniques will be investigated. A literature review is presented detailing conventional propellants, low vulnerability (LOVA) propellants and research into using TPEs as binders for propellants. In addition, the desirable mechanical and ballistic properties of propellants are assessed. The TPEs PEBAX, a polyether-block-amide (PEBA) and SEBS, a Styreneethylene/butylene-styrene were selected for analysis. A full assessment of the mechanical and thermal properties of these TPEs was conducted. They both have broadly suitable properties, however, both TPEs were substantially stiffer (greater storage modulus) than a typical binder and the lower glass transition for SEBS was above the desired minimum operational temperature. When plasticised with Dioctyl Sebacate (DOS), both PEBAX and SEBS had a reduction in the storage modulus and lower glass transition. PEBAX did not show any noticeable effect on the upper (melt) transition, conversely SEBS showed a larger reduction in the upper (glass) transition. SEBS was down selected for further evaluation due to its better availability, purity and greater solubility in solvents. Traditional mixing and manufacturing techniques where not suitable for processing of propellants with TPE binders. Slurry processing (used in manufacture of pressed PBXs) was selected to coat the filler, creating a moulding powder. This was replicated with a novel method using resonant acoustic mixing (RAM). The moulding powder was then consolidated by remote hot pressing to simulate an industrial extrusion or rolling process. This process was used to successfully manufacture two propellants using SEBS as the binder, AP/SEBS containing ammonium perchlorate (AP) as a filler and RDX/SEBS with RDX. Inert fillers of sugar and talc were trialled, and mechanical testing of these inerts was found to be generally in good agreement with the live fills. ii Initial combustion work on RDX/SEBS by closed bomb analysis at low pressure was indicative of good burning, with a low burn rate. Both AP/SEBS and RDX/SEBS were subject to thermal and mechanical analysis. This showed that the glass transitions (Tg) were only slightly changed from pure SEBS. In comparison to AP-composite propellants, both the storage modulus (E’) from DMA and Young’s modulus (E0) from tensile testing were substantially greater. The maximum stress (σm) was similar, however the maximum extension (εb) was less. With further optimisation, such as use of bonding agents, plasticisers, optimised particle size and improve manufacturing methods, it is believed that the maximum extension could be increased. Therefore a SEBS based propellant should deform less to an applied force, but still have a similar extension and hence elasticity to hydroxyl-terminated polybutadiene (HTPB) composite propellants. These theoretical improved mechanical properties should result in a safer propellant. This research has increased the knowledge and understanding of propellants based on commercially available TPEs. It is anticipated that this will be valuable in developing sustainable propellants of the future.Item Open Access Impact, penetration, and perforation of a bonded carbon-fibre-reinforced plastic composite panel by a high-velocity steel sphere: An experimental study(Professional Engineering Publishing, 2010-12-31T00:00:00Z) Hazell, P. J.; Appleby-Thomas, Gareth J.; Kister, G.In this work, the response of a bonded CFRP composite panel, manufactured by bonding two laminates together, to impact, penetration and perforation by a high-velocity steel sphere has been studied. The response of a relatively thick (c.a. 12 mm) laminate has been compared to similar data from [1] where relatively thin monolithic laminates were impacted by the same type of projectile. It was found that the ballistic performance of the system was increased over the impact energy range of interest when compared to these similar relatively thin composite laminates. Furthermore, both the energy absorbed per-unit-thickness of laminate and the level of damage as measure by C- Scan was similar when the panels were perforated at normal and oblique incidence. This raises the prospect of reducing experimental testing at oblique angles, if the behaviour at normal incidence is known.Item Open Access Manufacturing and characterisation of photoresponsive composites for defence applications(2017-12) Christogianni, P.; Moniruzzaman, M.; Kister, G.The development of composites with improved mechanical and impact resistance properties has attracted considerable attention within the defence and aerospace industries. These composites are finding applications in vehicle or aircraft structures which are frequently exposed to impact from bird strikes, hailstorm, dropped tools and runway debris. In addition, exposure to extreme conditions such as high levels of UV light exposure or extreme temperatures increases the brittleness of the polymer matrix, ultimately leading either to the loss of mechanical properties such as compression strength or even to the catastrophic structural failure of the composites. The aim of this PhD project was to develop toughened and self-healing composites in which delamination and crack growth can be managed to an acceptable level. This was attempted using a new epoxy-based resin modified with photoresponsive azobenzene. Mechanical properties of the composites, toughened by azobenzene, were improved as a result of the photo-induced changes in the azobenzene structures. Initial works were to identify, synthesise and characterise appropriate photoresponsive resins that were thought to offer composites with enhanced properties. The synthesis of azobenzene acrylic- and epoxy-based polymers were accomplished using conventional wet chemistry. Their properties were triggered by different stimuli and characterised using 1H NMR, UV/Vis and FTIR spectroscopy, DSC, GPC, rheology, and nanoindentation. The azobenzene/acrylic-based copolymer films showed a significant photomechanical behaviour. Nanoindentation analysis demonstrated a maximum increase in stiffness of 19% with an optimum azobenzene loading of 30 mol%. Such an enhancement in stiffness was attributed to the photoinduced reorganisation of the polymer chains by geometrical isomerisation (trans to cis isomers) of the azobenzene chromophores. Analysis of the thin films by optical microscopy demonstrated a healing effect of the indented region under UV irradiation suggesting that this class of polymers can be used as self-healing materials. Ultrasound was also found to trigger cis trans isomerisation in the solid state at a much slower rate (120-150 min) than by visible light (30-60 s). Azobenzene-modified epoxy resins were synthesised by optimising an existing synthetic route and their responses to light and curing behaviour with a common amine hardener (a curing agent for epoxy resin, used to initiate curing/hardening) were assessed. The resulting kinetic reactions were investigated using isothermal (95°C) and dynamic heating scans (30-180°C) in a DSC and by simultaneously monitoring the spectral information using a NIR-FTIR spectrometer. The modified epoxy azobenzene resin proved to be reactive enough to form a network that can withstand temperatures of up to 200°C. The azobenzene-epoxy resins exhibited high dimensional stability, stiffness enhancement and healing behaviour when they were exposed to UV light. Gas pycnometer studies demonstrated constant volume and density values of the resins before and after UV irradiation. Optical and atomic force microscopes were used to assess and quantify the healing effect of damaged azobenzene-based polymer films. An intrinsic healing (73% of the total damaged area) was caused by the UV-induced molecular mobility of azobenzene in a 3D crosslinked network. The influence of UV light and the effect of azobenzene loading on the epoxy-based polymeric matrices were also evaluated after fracture mechanics analysis and it was found that an 11% increase in fracture toughness was observed with 10 mol% azobenzene (without exposure to UV light). On the contrary UV light increased the brittleness of the matrix with higher azobenzene loading. The azobenzene-modified epoxy resin was used to produce glass fibre-reinforced composites. Their photo-induced properties were investigated by compression, impact and post-impact compression testing. The composites exhibited an increase (3-16%) in compressive strength after exposure to UV light due to the trans cis isomerisation. Moreover, it was demonstrated that the introduction of a small fraction of azobenzene (10 mol%) into the composites enhanced their impact resistance by 10% when subjected to high velocity impacts (190 m/s). The absorbed energy of the azobenzene composites which had been previously exposed to UV light was also increasing linearly with the azobenzene loading.Item Open Access Normal and oblique penetration of woven CFRP laminates by a high velocity steel sphere(Elsevier Science B.V., Amsterdam., 2008-05-31T00:00:00Z) Hazell, P. J.; Kister, G.; Stennett, C.; Bourque, P.; Cooper, G.In this research, two thicknesses of a woven CFRP laminate have been subjected to impact by a steel sphere in a velocity regime ranging from 170 to 374 m/s. Impact and penetration of targets at normal and oblique incidence were studied using high speed video. For the normal incidence targets at the higher velocities of impact, a conical mass of laminate was ejected ahead of the projectile. Furthermore, despite the energy transferred to the plate increasing with impact energy, the degree of delamination in the thicker targets decreased indicating a change in projectile penetration mechanism. Eventually, the degree of delamination in the thicker targets appeared to approach an asymptotic level whereas for the thinner targets the degree of delamination appeared constant regardless of impact energy. For oblique targets, more of the kinetic energy was transferred from the projectile when compared to the same thickness of target that had been subjected to a normal incidence impact. However, this was merely due to a geometrical effect. Further, thicker panels appeared to behave more efficiently by absorbing more kinetic energy per effective linear thickness at the lower impact energies where petalling is a dominant factor in the penetration. This advantage appeared to disappear as the impact energy was increased.Item Open Access Penetration of a woven CFRP laminate by a high velocity steel sphere impacting at velocities of up to 1875 m/s(Elsevier Science B.V., Amsterdam., 2009-12-31T00:00:00Z) Hazell, P. J.; Cowie, A.; Kister, G.; Stennett, C.; Cooper, G. A.The impact of a woven 6 mm thick CFRP laminate has been subjected to impact by an annealed steel sphere up to velocities of 1875 m/s. It was observed that above a threshold impact energy, the percentage of kinetic energy dissipated by the laminate was constant. Further, the level of damage, as measured by C-Scan and through-thickness microscopy remained roughly constant as the impact energy was increased. However, the size of the hole formed increased. This suggested that the energy transferred to the target in the velocity range of interest became independent of the delamination. Consequently, the main energy transfer mechanism at the high velocities of impact is thought to be due to the cavity expansion and more importantly, the kinetic energy of the particulates.