The Kassandra mining district in Chalkidiki is an important producer of base and precious metals in northern Greece. The mining district is comprised of two major Pb-Zn (Ag [plus or minus] Au) carbonate-replacement deposits at Olympias and Mavres Petres with total mineable reserves of 0.7 Mt Pb, 0.9 Mt Zn, 64 Moz Ag and 4.1 Moz Au. Skouries is a Cu-Au porphyry resource under development with reserves of 3.6 Moz Au and 0.8 Mt Cu. Despite available data, the geodynamic background of the polymetallic district mineralisation is unknown in the context of regional tectono-magmatic evolution. The scope of this PhD project was to develop an over arching ore-genetic model for the diverse mineralisation styles in the Kassandra mining district. The polymetallic zonation and spatial distribution of diverse mineralisation styles in the study area is characteristic for an intrusion-centred ore system. Subeconomic to economically important Cu-Au porphyry copper, Cu-skarn, Pb-Zn (Ag [plus or minus] Au) carbonate-replacement and basement-hosted Fe-Pb ([plus or minus] As) sub-epithermal vein mineralisation between Olympias, Mavres Petres, Madem Lakkos, Stratoni-Fisoka and Skouries represent the proximal to distal parts of a fault-controlled magmatic-hydrothermal system. Fluid inclusion and stable isotope data provided by previous authors identified magmatic and evolved meteoric-hydrothermal fluids in the mineralisation system. New He and S stable isotope data support the involvement of a magmatic component as important metallogenic source for metals, ligands, fluids and heat. Spatially and genetically related to the mineralisation are Oligocene-Miocene stocks and dykes of granite, granodiorite diorite, diorite-gabbro and subordinate gabbro. U-Pb zircon and [sup]40Ar-[sup]39Ar mica ages constrain the mineralisation-related calc-alkaline, medium-K to shoshonitic magmatism to a short-lived cycle between 29 Ma and 20 Ma. A late Oligocene [sup]187Re-[sup]187Os isochron age of 26.1 [plus or minus] 5.3 Ma for ore-related arsenopyrite from the Olympias deposits provides a robust in-situ formation age for the carbonate-replacement mineralisation in the district. Two [sup]40Ar-[sup]39Ar biotite ages of 26.3 [plus or minus] 0.3 Ma and 19.9 [plus or minus] 0.2 Ma date the porphyry-style mineralisation-alteration at Stratoni-Fisoka and the economically important Skouries Cu-Au porphyry resource. Magmatism and magmatic-hydrothermal mineralisation in the district were coeval with a phase of post-collisional extension in the North Aegean region. Eocene-Miocene slab roll-back initiated orogen-scale lithospheric stretching, crustal thinning and asthenospheric upwelling which elevated the regional heat gradient. Heat transmission into lower structural levels of the Rhodope nappe pile started and maintained hydrothermal fluid circulation which led to the formation of base metal rich-deposits. Metamorphic and protolith ages of host and country rocks allocate the district mineralisation to the middle to upper tectono-stratigraphic crustal levels. Here, on the flank of the Southern Rhodope core complex, the heat flux was not high enough to initiate large-scale fluid flow. Instead, synetensional partial melting at mid to lower crustal levels, involving fertile and hydrous cumulates in the subduction-modified sub-continental lithospheric mantle, generated hydrous melts with subduction-type chemical signatures that were emplaced in the Kassandra mining district in the magmatic arc above the retreating slab.

The aim of this thesis is to model the extrusion process conditions for some aluminium alloys using Finite Element Modelling (FEM) program. All the simulations were performed with the implicit finite element code FORGE20 (2-D) and FORGE3® (3-D). In this work only the alloys AA2024, AA2014, Al-1 %Cu and AA6063 where experimental work is available were considered. The FORGE2® program was used to investigate and select an appropriate flow stress constitutive equation to describe the material behaviour to model the process conditions. The extrusion pressure and the temperature rise were predicted and the pressure-displacement trace and the events which take place in the deformed material during the extrusion process were also simulated. The effect of the initial billet temperature on friction, and the extent of the surface zone affected by surface friction and the consequence changes in material flow were investigated. The changes in the subgrain size during quasi-static deformation were predicted. This allows a construction of velocity-displacement profiles which would ensure consistent properties over the length of the extrudate. The FORGE3® program was used to simulate the effect of changing the die geometry on material flow during extrusion for rod, shapes and tube extrusion and the effect of the initial temperature on the deformation zone. The load required, temperature evolution, surface formation of the extrudate and material flow during the process, were also predicted. These included solid sections and the production of tubes using bridge die. Two most commonly used constitutiveflow stress equations,the Zener-Hollomon and the Norton-Hoff were analysed and compared with experimental results. It was found that the Zener-Hollomon relationship provided a better representation of the experimental flow stress under high working conditions than the Norton-Hoff relationship. FEM has been successfully applied to model the deformation patterns in the load/displacement traces and temperature evolution during the extrusion cycle. The effect of the initial billet temperature on the deformation zone pattern and its consequent effect on friction using both numerical simulation and experimental work are presented. A specific function relationship to measure directly interfacial friction under conditions approaching those encountered in the quasi-static deformation process is described. The results revealed that the friction factor increases with increase in initial billet temperature and varies during the extrusion cycle. The dead metal zone (DMZ) is observed to vary in form and has a greater volume at high temperatures. FEM proved to be a very effective and efficient way to design the ram speed profile to control the extrudate properties. The control of the properties of the extrudate under a constant (Z) parameter resulted in a more uniform distribution of the subgrain size across and along the extrudate cross-section. Furthermore, the speed profile under constant Z conditions resulted in an improved extrusion speed and hence greater productivity coupled with better control of the subgrain size and the exit temperature. This new extrusion process is termed iso-Z Extrusion, and is considered an improvement on Iso-Thermal extrusion. The usefulness and the limitation of FEM when modelling complex shapes are discussed. Methods to assess the difficulty of hollow and section shapes are presented. The work also illustrates the essentials of numerical analysis in the comprehension of the thermo-mechanical events occurring during extrusion through bridge and shape dies. Results are presented for velocity distribution in the extrusion chamber, Iso-temperature contours and pressure/displacement traces. It is shown that for most of the shapes investigated, the material making up the extrudate cross-sections originated from virgin material within the billet. The outside surface of the extrudate originates from the material moving along the DMZ and the core of the extrudate from the central deformation zone. When simulating tube extrusion, it is shown that the FE program is able to predict the pressure requirements: the pressure/displacement trace showing a double peak for tube extrusion which is discussed in some detail. The FE program appears to predict all the major characteristics of the flow observed macroscopically.

The aim of this researchis to use advanced materials and state of the art Finite Element Analysis to produce a novel acetabular cup prosthesis. An investigation into current static and fatigue testing procedures for acetabular cup prostheses has identified current strengths and weakness and proposes a cheap, fast method that is closer to anatomical loading conditions. The current trend of performing Total Hip Replacements(THR) on younger patients incurs an increasing number of revisions. Therefore, prolonging the life of a THR is of paramount importance and is the principal goal of this study. With this trend comes a new set of design goals driven by higher patient expectations of their THR. Younger patients not only require increased longevity from their prosthesis but also increased performances so as to be able to undertake more strenuous everyday activities, such as sports. Historically, the main objective of THR was to relieve pain and increase quality of life in the elderly and was not intended for young active patients. Previous research proposes that the acetabularcup design has far more impact on long-term survival of the THR than the femoral component. Optimising the acetabular cup prosthesis produces a highly complex problem where many of the individual design factors have massive impact on the system. A main aim is to develop a material or combination of materials to optimise the stress distribution in the system without sacrificing the service life of the THR. Of the 800,000 hip replacements carried out annually, many of the current acetabular cups have some form of polyethylene bearing surface. However, polyethy lenewear debris is seen as a major contributing factor to bone resorption and hence prosthesis loosening. Changes in stress values, even caused by initial primary fixation during the operation, can result in stresses being transferred in an unrealistic manner. The effect is that the bone grows to differing thickness and strengths. This is known as remodelling. For optimisation of the acetabular cup, the properties of the natural hip must be retained by minimising both remodelling and bone resorption. The present research, with collaboration from Orthodynamics Ltd., has produced novel composite acetabular cup prostheses with a ceramic on ceramic bearing surface that should last longer and perform better, thus reducing the necessity for costly and debilitating revisions later on in life. In addition, the use of the proposed novel anatomically orientated mechanical testing methods gave fast,cheap results and could also allow further research into fatigue failure of alumina bearing couples in THR.

Research to understand the mechanisms of wear within the main components of three different micro-CHP scroll expander systems was conducted. This was performed in order to identify the possible tribo-mechanical effects (abrasion, adhesion, cavitation, fatigue) which occur on the substrate of these components during the operation of the scroll which can seriously affect the lifecycle of the micro-CHP unit. Three-dimensional interferometer, surface scanning and scanning electron rnicroscopy (SEM) were used for surface analyses. The critical components for durability were identified on the tip seal and the steel plate of the scroll expander. Abrasive wear derived from a two-body contact on the interface of the tip seal and the steel plate. Three-body wear was found across the steel plate of the scroll. Finally, cavitation pits were revealed. Interestingly, cavitation was generated by the increment of pressure. It was found that sufficiently high pressure can liquefy instantaneously part of the refrigerant close to the bottom boundary, creating conditions for the generation of cavitation bubbles within the liquefied refrigerant. This finding resolves the puzzle of how the refrigerant which enters the scroll in gas phase produces cavitation. The wear mechanisms identified can significantly reduce the performance of the scroll. Specimens made from the steel plate (high carbon steel) and the tip seal (high performance reinforced fluoroelastomer) of the scroll expander were used for bench tests. The parts were used to perform sliding tribological tests using a special purpose-built modified micro-friction machine TE 57 in order to clearly identify the sliding wear and friction mechanisms. These tests were performed under a specific load and lubrication regime. The experimental conditions were adjusted to those of the industrial applications. Furthermore an experimental study using an ultrasonic transducer (submerged into the fluids) was utilised to produce cavitation bubbles. Using high-speed camera techniques the bubbles were observed within the working fluids. A thorough investigation of the dynamic behaviour of the bubbles and their cavitation mechanisms was conducted using the two scroll fluids (lubricant/refrigerant). The experimental results were effectively correlated with the computational ones. Additionally, the impact of the scroll fluid cavities across the surface of various commercial steel grades, including the actual steel plate of the scroll, was determined. Finally, their cavitation performance and durability, over a prolonged period of time was investigated.

Research concerning the surface of technical ceramics is carried out from the viewpoint of their mechanical performance subjected to relevant operating conditions. The selected materials are silicon nitride, zirconia and alumina. They are subjected to cavitation erosion and other wear processes. When polished ceramics are subjected to cavitation, a pseudoplastic deformation pit is discovered, as well as a delayed phase transformation or ageing of the zirconia stored at room temperature. Measured ageing times recorded are of the order of one month. These two discoveries are novel and a full explanation is explored. The creation of cracks that release the slip planes of ceramic grains allowing plastic deformation is proposed to be the main mechanism. In order to understand the relationship of the zirconia surface degradation with its oxides (yttria or magnesia), several material compositions are tested. It is concluded that the delay of phase transformation relies on the existence of partially stabilized tetragonal zirconia regardless of the oxide used to stabilize it. Part of this research consists of understanding the effects of the experimental procedure that is utilised on the behaviour of the material. An unexpected non homogeneous cavitation erosion shape is obtained when an ultrasonic horn of small diameter is used to produce the bubbles. This non homogeneous region, referred to as ring region for this research, affects the erosion pattern of the material and it differs from the typical ones obtained when following the standard test. The acoustic theory does not explain this phenomenon. Therefore, a new approach is followed. This approach consists of using fluid mechanics equations combined with analytical mechanics principles. It is concluded that the location of cavitation clusters fulfils a condition of minimum energy. On the other hand, there are important differences between this experimental set up and the set up suggested by the published standards. These differences are discussed and a criterion for cavitation erosion resistance is developed. The comparison of cavitation resistance of materials is achieved by means of surface loss as criterion instead of volume loss.

This thesis reports the analysis by FEM of both continuum and structural models describing the extrusion process. They were compared with experimental work and the agreement is satisfactory. All the simulations were performed with the implicit finite element code Forge2009® with user input written in Visual Fortran®. Alloys AA2024 and AA6063 were utilised as the source materials in order to compare with published experimental work. The Forge2009® 2D module was used to investigate both direct and indirect axisymmetric rod extrusions. The extrusion load and the temperature rise were predicted and the load-displacement curves and the events that took place in both extrusion modes were also simulated, discussed and again verified. The effects of the difference between the two modes, especially friction and its consequences on the process were investigated. The indirect results point to a good method of improving efficiency. For complex solid section, the 3D module has been used to study the load required, temperature evolution, surface formation of the extrudate and material flow during the process. These all showed good correlation with experimental results. The microstructure evolution during the extrusion process and the following solution soaking process were simulated with physically-based mathematical microstructure models integrated into FEM through its Fortran® subroutine interface,. The agreement between the predicted microstructures using associated models and experimental measurements were acceptable. For hollow section, the emphasis was placed on the study of the complicated metal flow and the seam welding quality. Novel analyses were developed to analyse the metal flow.

This thesis reports the analysis of extruded products by Forge2009® and EBSD produced by the investigator in the BOAL plant. The 3D FEM module was used to study the required load, the temperature evolution, surface formation of the extrudate and material flow during the process. The effect of varying process conditions on the selected geometries were investigated and verified by means of experiment. Considering the difficulty in performing the experiments (high temperature and high strain rates) the simulation results can be considered to be acceptable. The simulations were performed with the implicit finite element code Forge2009® with user input written in Visual Fortran®. Alloy EN AW-6082 was selected on the basis that is a commonly used extrusion material in industry. A range of simulations were designed which would produce differing structures to those experienced within the industry. The effect of variation of the bridge design for hollow dies and the effect of variation of the sink in for solid dies was investigated. 3D simulations were performed to investigate the effect of these variations in the design features on extrusion process parameters. The process parameters which are likely to be affected are load, deflection, velocity and temperature. The results indicated that the design of the die affected the process parameters. The microstructure evolution during the extrusion process was investigated for the selected complex geometries. The following microstructure features were included in the investigations: Recrystallised grain size, subgrain size, misorientation, dislocation density and volume fraction recrystallised. Simulations were performed using physically-based mathematical microstructure models integrated into FEM through its Fortran® subroutine interface. Experiments were performed to investigate the effects of varying process conditions on the microstructure. For hollow section, the emphasis was placed on the study of the complicated metal flow and the seam welding quality. EBSD analyses were performed to investigate the substructure. Surface cracking was modelled and compared with experiments. The agreement between the predicted microstructures using associated models and experimental measurements were acceptable. Predicted cracking show good correlation with experimental results.

One remarkable advantage of hybrid bearings over all steel bearings is the elimination of separate oil lubricant system in applications, such as compressors and pumps in refrigeration and air conditioning units. High speed test runs restricted increase in speed due to material wear, which eventually affected the life of bearings. Being low saturation temperature fluids, change of phase is very common in refrigerants and cryogenic liquids, which lead to cavitation. Silicon nitride rolling elements with different sintering additives, properties and microstructure were experimentally studied to understand the nature of cavitation erosion. Advanced surface analysis technique was used study the erosive wear correlation to microstructure of test materials. Cavitation erosion wear initiated by multiple intergranular and transgranular fracture, leading to erosion pit formation. Grain size and grain boundary composition have shown to be the dominant factors for providing resistance to cavitation. Effect of surface defects and lubricant viscosity on cavitation erosion was investigated and is detailed in this thesis. A rotary specimen method was designed to study the effect of cavitation on rolling bodies. Computational modelling of acoustically generated cavitation was attempted and is also reported in this work. A novel test methodology was designed and manufactured by modifying a rotary tribometer to allow controlled experimental testing of two different phenomena rolling contact fatigue and cavitation erosion. This testing made it possible to study rolling and erosive wear mechanisms of rolling elements. Cavitation created far away in this new system is shown to be transported to the rolling contacts. The mechanism of material damage was by surface weakening due to mechanical impact of bubbles, which enhance fluid entrance and hydrodynamic pressure leading to wear initiation. Micro erosion pits formed in the rolling contact, which accelerated the damage by dislodging grains and bunch of grains. This testing method is suitable for a qualitative assessment of cavitation-RCF damage for different fluids with varying viscosities, and operating conditions.

No description available.

Polymers and polymer-based composite materials with electrically-conductive properties are materials with various potential uses. Novel materials are becoming available in each field and new products are continuously being produced. Amid these new materials, conductive elastomers are presently being employed as antistatic materials in the carpets, antistatic coatings, sensors and electromagnetic screening. One promising method for making this type of material is to introduce carbon black or metal fillers, or more currently conducting polymer powders into natural or synthetic rubbers. Several polyaniline-rubber blends, mostly with poor electrical conductivity, have been reported in the literature. An important aim of this work was to improve the compatibility, thermal stability, electrical and mechanical properties of this kind of blend, produced by different mixing techniques for instance solution and thermo-mechanical with further methodical mixing processes and greater improved mixing circumstances. Polyepichlorohydrin, polychloroprene rubber, chlorosulfonated polyethylene rubber and polyaniline dodecylbenzenesulfonate (PAni-DBSA) were selected for study as blends in this project, since the solubility parameters of polyepichlorohydrin rubber, polychloroprene, chlorosulfonated polethylene and polyaniline dodecylbenzenesulfonate were calculated to be well-matched, and also because the polyepichlorohydrin rubber (PECH), polychloroprene rubber (PCR) and chlorosulfonated polyethylene (CSPE) were thermally stable and easily obtainable. No previous literature was discovered in relation to the electrical properties of the polyepichlorohydrin, polychloroprene or chlorosulfonated polyethylene blends with polyaniline dodecylbenzenesulfonate (PAni-DBSA). Hence, the PECH, PCR and CSPE rubbers were also chosen in this work with the purpose of studying them. Non-vulcanised PECH/P Ani-DBSA, non- vulcanised PCRlPAni-DBSA and non-vulcanised CSPEIPAni-DBSA blends with appropriate electrical conductivities were produced by solution mixing for the first time in this project. Blends of the PECH, PCR and CSPE rubbers and polyaniline doped with dodecylbenzenesulfonic acid, consisting of various proportions of P Ani- DBSA, were cast from solution onto polytetrafluoroethylene (PTFE) substrates with the aim of making electrically conductive films. Electrical conductivities of the cast films of non-vulcanised blends were calculated. Decomposition steps of electrical conductive polymer blends were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The thermal stabilities of the PECHlPAni-DBSA, PCRJPAni-DBSA and CSPEIP Ani-DBSA blends were affected by the proportion of polyaniline dodecylbenzenesulfonate to the rubbers. The influence of composition on the glass transitions in the blends was defined by the use of thermomechanical analysis (TMA). Electrically conductive polymer blends of vulcanised PECHIPAni-DBSA were prepared by the use of an internal mixer for the first time. A remarkable agreement was seen in that both the vulcanised and the nonvulcanised blends had the electrical conductivities of the order of 10-8 S.cm-1 with approximately 20 wt% polyaniline dodecylbenzenesulfonate. The electrical conductivities of all the vulcanised PECHIP Ani-OBSA blends (with a conductivity percolation threshold 1 wt% or 1.07 vol % of P Ani-OBSA) were riot influenced by the addition of Zisnet-F as the vulcanizing agent. The ATIR spectra of vulcanised PECHIPAni-OBSA blends were similar to a superposition of the spectra of the pure vulcanised polyepichlorohydrin and pure polyaniline dodecylbenzenesulfonate, but with some distinctive peak shifts due to the changing intermolecular interactions among the PECH and PAni-OBSA polymers. The X-ray diffraction patterns of polyaniline dodecylbenzenesulfonate, the vulcanised pure polyepichlorhydrin and vulcanised polyepichlorhydrinl polyaniline dodecylbenzenesulfonate blend with 10% of PAni-OBSA were studied. The effects of addition of the polyaniline dodecylbenzenesulfonate on the morphology of the vulcanised PECHIP Ani-OBSA blends were evaluated by optical microscopy. The influence of orientation and alignment of the PAni-OBSA particles on the mechanical and electrical properties of vulcanised blends was investigated. The electrical conductivities of all vulcanised polyepichlorhydrin/polyaniline dodecylbenzenesulfonate blends were identified by stretching them. All vulcanised PECHIPAni-OBSA blends strained parallel to the flow direction when passed through the two roll-mills had their electrical conductivities improved with increasing strain in tension. A traveling microscope was used to investigate any possible dimensional change of samples versus applied voltage in order to define the effect of voltage to size change of the vulcanised blends. The electrical percolation threshold stage for the vulcanised PECHIP Ani-DBSA blends was studied. A tensile testing machine was employed to determine energy storage of each vulcanised PECH/P Ani-DBSA blend. Tensile property testing for the vulcanised polyepichlorhydrin /polyaniline dodecylbenzenesulfonate blends was accomplished according to the British Standards Institution (BS!) requirements in order to measure tensile strength, elongation at break and tensile modulus, and the samples all presented good mechanical properties. The stress-strain data of the vulcanised polyepichlorhydrin /polyaniline dodecylbenzenesulfonate blends have been analyzed and the crosslink density of them has been calculated. With good mechanical properties and reversible electrical behaviour, this kind of vulcanised blend may potentially be developed as a novel class of flexible smart material.