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In the framework of the High-Luminosity Large Hadron Collider (HL-LHC) project, a complex structure, known as the beam screen, will be installed by 2024 in the aperture of the inner triplet superconducting magnets nearby the ATLAS and CMS experiments. The beam screen is an octagonal shaped pipe that shields the 1.9 K magnet cryogenic system from the heat loads and damage to the magnet coils that would be otherwise induced by the highly penetrating collision debris. It also ensures that the vacuum conditions, required for the stability of the beam, are met. This thesis describes the design of the beam screen and proposes extensions to important components and features. The unknown physical properties of the beam screen materials have been characterised. The thermal behaviour of the beam screen during normal working conditions has been optimised by simulations and validated by measurements. The behaviour of the beam screen during a magnet quench, a resistive transition of the superconducting magnet, has been studied. Two magnet quench protection systems have been considered: the Quench Heaters (QH) by themselves and in conjunction with the Coupling Loss Induced Quench (CLIQ) device. To this purpose two innovative coupled multiphysic models have been developed, which have been verified by comparison with a closed form expression showing the advantages of considering self-inductance phenomena. In the case of the QH the force distribution per quadrant gives rise to forces up 330 N/mm in the beam screen closest to the interaction point, while in the case of the CLIQ a torque load-type is induced, whose maximum intensity is around 2 N m/mm. With the new multiphysic models an unprecedented level of accuracy has been achieved, which has permitted to demonstrate the mechanical integrity of the proposed beam screen design during a quench.

The demand for drastic reduction in CO2 emission among road vehicles has seen downsizing becoming a megatrend in modern engine developments due to its benefits in reducing throttling loss and improvement in engine efficiency. In light of this, turbocharging is seen as one of the key enabling technologies and therefore carries along with it an ever-increasing challenge in terms of system-matching as the device is required to operate in ranges never encountered before. The increasing reliance on 1-D engine performance simulation tools calls for more accurate representation of the turbocharger model. The present study assessed the turbocharger turbine maps for use in commercial 1-D gas dynamics engine code from several aspects, namely the width of the map and the representation of turbine unsteady performance in the virtual environment. Furthermore, the present work assessed the performance of turbine under waste-gated operations. For this, an experimental work has been carried out on a bespoke waste-gated turbine layout over a wide range of operating conditions. The performance of the radial turbine under steady inlet conditions was evaluated for different waste-gate openings, at various points along several speed-lines. Then the unsteady tests saw the turbine performance evaluated at various sets of pulse frequencies, turbine loadings and waste-gate openings. Analysis of this study include the impact of turbine map width on the turbine performance modelling in a commercial 1-D gas dynamics engine simulation software and subsequently the prediction of the engine’s performance. This simulation work is carried out based on an actual heavily downsized gasoline engine with a series super-turbocharging system. The study also examined the method of incorporating the effects of turbine unsteady performance under waste-gated and non-waste-gated conditions in the performance maps used in 1-D code and evaluate its impact on the engine performance prediction. The outcome of the study aims at providing a deeper understanding on the unsteady performance of a turbocharger turbine which will lead to improved turbocharger-engine matching methods in the future.

The need for smarter and active, energy absorbing systems designed especially for human protection applications has sparked interest in highly strain rate sensitive compounds. This thesis describes the iterative design, development and optimisation of a novel form of energy absorbing, body worn protection. The original contribution to knowledge is the development of a novel strain rate sensitive protection system incorporating synergetic internal architecture. Co-continuous blends of silicone based dilatant and thermoplastic elastomer have been developed through a recursive design process to develop a new material specifically optimised for body worn protection. Failure mechanisms were analysed, and from these results techniques have been developed to mitigate internal fracture mechanisms. This enabled the development of a strain rate sensitive material utilised with an internal architecture. The novel material properties were examined and developed using monolithic samples, tested at a variety of energies, speed and environmental conditions. Methods for designing and developing auxetic structures that work synergistically with the new material have been developed. The novel system has also been combined with textiles, and the merit of this combination explored. An improvement in performance has been validated, as well as a design improvement through being able to attach parts directly to garments. The resulting impact protectors are applicable over a range of strain rates. Systems have been designed to incorporate this novel technology in pre-production prototypes in three selected market areas, which typify low, medium and high impact speeds. The work also explores the systems ability to manage multiple impacts at the same location with a surprisingly low loss in performance, effectively making a protector that can withstand repeat impacts. This work has contributed to the methods previously used in testing personal protective equipment. The techniques developed in this work have enabled new revision of these PPE standards, as well as directly contributing to two new standards.

Environmental concerns have prompted research into natural materials to improve sustainability. Cellulose has some of the highest mechanical properties among naturally-derived materials, and natural-fibre composites have better specific stiffness than glass-fibre composites, and are thus increasingly used in the transport and construction sectors. However, cellulose is hydrophilic and it is difficult to obtain a uniform dispersion of cellulose modifiers in epoxy polymers. This makes it challenging to achieve high performance natural-fibre composites with good delamination resistance, which is critical in composite applications. Therefore, in the present study, the toughening effect of cellulose modifiers in an anhydride-cured diglycidyl ether of bisphenol-A (DGEBA) epoxy polymer, and in regenerated cellulose-fibre (CeF) composites are investigated. The cellulose modifiers initially agglomerated and sedimented in the epoxy. However, the addition of a silane during the three-roll mill process resolved this issue, and a good dispersion of cellulose modifiers was achieved. The addition of 10 wt% of cellulose modifiers, i.e. microcrystalline cellulose (MCC) and cellulose nanocrystals (CNCs), increased the fracture energy (GC) of the epoxy by more than 100 %, compared with 57 % for nanosilica, which is a well-studied and effective epoxy toughener. Hybridisation of MCC and CNCs with nanosilica or rubber particles, i.e. carboxyl-terminated butadiene-acrylonitrile (CTBN) and core-shell rubber (CSR), generally yielded additive toughening effects since the toughening mechanisms associated with each modifier were largely still present in the hybrids. To assess the effectiveness of the transfer of the increased matrix toughness to fibre composites, plain-weave CeF composites were fabricated using the wet layup process. Their mode I interlaminar fracture energies were compared with the bulk fracture energies, and their properties were benchmarked with glass-fibre (GF) composites. Although GF composites have better tensile properties than CeF composites, the composite propagation fracture energies (GC,prop) of CeF composites (e.g. control-CeF: 1155 J/m2) were about twice those of GF composites (e.g. control-GF: 567 J/m2). This was due to more extensive fibre bridging and crack branching behaviours. Analytical models showed reasonably good agreement with the experimental GC for the epoxy polymers, GF composites and CeF composites. These models were able to predict the significance of various fibre and matrix toughening mechanisms identified through fractography, which also correlated well with experimental observations. The highest GC,prop values obtained for the GF and CeF composites were 901 ± 102 J/m2 and 1537 ± 56 J/m2, respectively, which are 59 % and 33 % higher than their respective control composites. It was found that the GC,prop values did not increase further when matrices with higher toughness were used. Hence, cellulose modifiers can be used to replace nanosilica in hybrid matrices to obtain GF or CeF composites with reasonably high fracture energy and increased renewable content.

Stress distributions around fibre discontinuities in a composite material have been investigated by idealised two-dimensional models. These models have been analysed by the finite element method using a digital computer. Aluminium fibre/epoxy resin matrix models have been examined photoelastically to verify the elastic analyses and a steel fibre/lead alloy matrix model has been studied using the photoelastic coating and moire methods to verify the elastic/plastic analyses. It has been found that a fibre discontinuity is a source of severe matrix stress concentration, in excess of that associated with a single fibre end. The magnitude of this stress concentration and the corresponding length of fibre in which the axial stress is below the fully developed value depend upon the size and nature of the discontinuity (i.e. whether void or matrix filled), the inter-fibre spacing and the fibre/matrix modulus ratio. The fibres adjacent to a discontinuous one carry an elevated load the magnitude of which depends upon the same parameters. The elastic/plastic analyses show that matrix yielding reduces the stress concentration in the matrix by increases in the fibre stresses and the area of stress perturbation. The results of these stress analyses are compared with the experimental observations of other workers and discussed in relation to published theories of failure. It is concluded that if the effects of a fibre discontinuity can be kept localised by having a ductile matrix or weak fibre/matrix interfaces the composite behaves in a quasi-homogeneous manner and its strength can be predicted by existing theories.

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