An Evaluation of Geomechanical Properties of Potential Shale Gas Reservoirs in the Lower Indus Basin, Pakistan

Pakistan has been facing a growing energy crisis for the last decade, and the government is seeking new horizons for enhancing oil and gas production to reduce the gap between supply and demand. Although several shales of the Indus Basin in Pakistan are known source rocks for conventional hydrocarbon reservoirs, data currently available to assess their potential as shale gas reservoirs are somewhat limited. The objective of this research was to investigate, assess and improve methods for geomechanical characterization of shales using standard datasets of the type available (in the public domain) for Indus Basin shales. In this research, six shales which are known to be source rocks in the Indus Basin, Pakistan, were evaluated for their shale gas potential by comparison against several of the most active shale gas plays in North America. The comparison included available geological, geochemical, petrophysical and elastic properties, and concluded that all of the Pakistani shales investigated are promising regarding their shale gas potential. However, more petrophysical and geomechanical data are required before conclusions about these shales can be made with greater confidence. In light of this, the remainder of the research conducted in this project focused on applying (and improving) advanced interpretation techniques on two of the prospective Lower Indus shales deemed to have the best available (public domain) data. The interpretation of geomechanical properties generally requires knowledge of sonic shear wave velocity (Vs). Given that Vs measurement is commonly omitted from routine geophysical logging suites, many investigators have developed empirical models and rock physics models of varying form and complexity for the estimation of Vs using available well log and/or core analysis data. This study evaluated various relationships in the literature for the estimation of shear wave velocity applied to sandy shale and shale intervals of the Lower Goru Formation, Lower Indus Basin, for which two wells with Vs data were available. The results reveal that some empirical models can be effective for estimating Vs, but only when the model coefficients are adjusted by calibrating to site-specific Vp and Vs data. A modification to rock physics modeling developed for this type of work demonstrated that the use of Biot’s model (rather than Gassmann’s model) for fluid substitution improved model performance for Vs estimation in gas-saturated sandy shale and shale of the Lower Goru Formation. The rock physics-based model offers the advantage of being useful in settings where only Vp data are available for model calibration, and it is suggested that the rock physics model should be reliable when applied to a broader range of saturations and lithologies in the Lower Goru Formation. The next phase this work involved characterization of a shale interval in the Early Cretaceous-age Sembar Formation, Lower Indus Basin of Pakistan, using only readily available data. A workflow was developed for the estimation and mapping of geomechanical properties using logs from multiple wells and relevant post-stack seismic reflection data. Mineralogy data from well cuttings, core testing results for elastic properties and hydraulic fracturing test data were utilized to constrain the values of the properties estimated from geophysical data. The following results obtained at the well-scale suggest that the Sembar Shale is favorable for development: high gas saturation, good porosity (up to 10%), moderate quantity of thermally mature organic matter (2% - 4% TOC), a number of brittle intervals separated by thicker intervals that fall slightly below the brittle-ductile threshold, and a strike-slip stress regime. At the scale of the study area, robust statistical techniques were used to invert seismic stacks and develop a 3D mechanical earth model. This model shows a trend of increasing shale brittleness towards the northeastern portion of the study area, hence suggesting that this area might be most prospective for initial shale gas development. The final phase of this research involved the assessment and improvement of techniques for estimating mechanical properties using drill cuttings, which serve as the only available basis for laboratory testing when core samples are unavailable. Microindentation testing was selected for this work based on the literature review. Experimental techniques developed or improved in this work include: embedding multiple cuttings into an epoxy puck to facilitate sample preparation, mineralogical analysis, and testing of a large number of sampling points; progressive re-saturation to restore cuttings to in-situ moisture conditions; selection of optimal indentation force; assessment of sample anisotropy; brittleness assessment based on indentation morphology; (and a statistical / rock physics framework for estimating macroscopic properties from extensive testing of samples with variable mineralogy). Limitations of this testing method are discussed, as are recommendations for future research

An Evaluation of Geomechanical Properties of Potential Shale Gas Reservoirs in the Lower Indus Basin, Pakistan

Pakistan has been facing a growing energy crisis for the last decade, and the government is seeking new horizons for enhancing oil and gas production to reduce the gap between supply and demand. Although several shales of the Indus Basin in Pakistan are known source rocks for conventional hydrocarbon reservoirs, data currently available to assess their potential as shale gas reservoirs are somewhat limited. The objective of this research was to investigate, assess and improve methods for geomechanical characterization of shales using standard datasets of the type available (in the public domain) for Indus Basin shales. In this research, six shales which are known to be source rocks in the Indus Basin, Pakistan, were evaluated for their shale gas potential by comparison against several of the most active shale gas plays in North America. The comparison included available geological, geochemical, petrophysical and elastic properties, and concluded that all of the Pakistani shales investigated are promising regarding their shale gas potential. However, more petrophysical and geomechanical data are required before conclusions about these shales can be made with greater confidence. In light of this, the remainder of the research conducted in this project focused on applying (and improving) advanced interpretation techniques on two of the prospective Lower Indus shales deemed to have the best available (public domain) data. The interpretation of geomechanical properties generally requires knowledge of sonic shear wave velocity (Vs). Given that Vs measurement is commonly omitted from routine geophysical logging suites, many investigators have developed empirical models and rock physics models of varying form and complexity for the estimation of Vs using available well log and/or core analysis data. This study evaluated various relationships in the literature for the estimation of shear wave velocity applied to sandy shale and shale intervals of the Lower Goru Formation, Lower Indus Basin, for which two wells with Vs data were available. The results reveal that some empirical models can be effective for estimating Vs, but only when the model coefficients are adjusted by calibrating to site-specific Vp and Vs data. A modification to rock physics modeling developed for this type of work demonstrated that the use of Biot’s model (rather than Gassmann’s model) for fluid substitution improved model performance for Vs estimation in gas-saturated sandy shale and shale of the Lower Goru Formation. The rock physics-based model offers the advantage of being useful in settings where only Vp data are available for model calibration, and it is suggested that the rock physics model should be reliable when applied to a broader range of saturations and lithologies in the Lower Goru Formation. The next phase this work involved characterization of a shale interval in the Early Cretaceous-age Sembar Formation, Lower Indus Basin of Pakistan, using only readily available data. A workflow was developed for the estimation and mapping of geomechanical properties using logs from multiple wells and relevant post-stack seismic reflection data. Mineralogy data from well cuttings, core testing results for elastic properties and hydraulic fracturing test data were utilized to constrain the values of the properties estimated from geophysical data. The following results obtained at the well-scale suggest that the Sembar Shale is favorable for development: high gas saturation, good porosity (up to 10%), moderate quantity of thermally mature organic matter (2% - 4% TOC), a number of brittle intervals separated by thicker intervals that fall slightly below the brittle-ductile threshold, and a strike-slip stress regime. At the scale of the study area, robust statistical techniques were used to invert seismic stacks and develop a 3D mechanical earth model. This model shows a trend of increasing shale brittleness towards the northeastern portion of the study area, hence suggesting that this area might be most prospective for initial shale gas development. The final phase of this research involved the assessment and improvement of techniques for estimating mechanical properties using drill cuttings, which serve as the only available basis for laboratory testing when core samples are unavailable. Microindentation testing was selected for this work based on the literature review. Experimental techniques developed or improved in this work include: embedding multiple cuttings into an epoxy puck to facilitate sample preparation, mineralogical analysis, and testing of a large number of sampling points; progressive re-saturation to restore cuttings to in-situ moisture conditions; selection of optimal indentation force; assessment of sample anisotropy; brittleness assessment based on indentation morphology; (and a statistical / rock physics framework for estimating macroscopic properties from extensive testing of samples with variable mineralogy). Limitations of this testing method are discussed, as are recommendations for future research

Characterisation and Evaluation of Thermally Treated Recycled Glass for Mass Finishing and Superfinishing Processes

This thesis presents the work on the characterisation and evaluation of an entirely new mass finishing product based wholly on thermally treated recycled glass, which acts as both a bond and abrasive for mass finishing and superfinishing processes. The recycling of glass is excellent in respect of sustainability and environmental efficiency. The aim of the study was to establish requirements for the high volume manufacture of thermally treated recycled glass preforms to satisfy stated performance criteria. Several powder characterization techniques were employed to assess morphology and flowability of various grades of soda lime glass powder. The results obtained have demonstrated that flowability and packing properties improve with an increase of particle size. Thermal analyses were successfully employed for various types of mould material to determine the optimal glass powder size in terms of crystallinity and mechanical properties. It was found that by controlling the time transformation temperature TTT relationship, it is possible to consistently produce abrasive media possessing particular mechanical and physical properties that deliver target mass finishing performance. The residual stresses developed during different thermal cycles were investigated numerically and experimentally. Compressive stress was observed near the media edge and tensile stress in the mid-plane at the end of the solidification process. The results showed that the numerical FEA code is a suitable tool for the prediction of residual stresses of thermally treated recycled glass. A study concerned with the tip geometry of the Vickers and Berkovich indenters was completed to ensure an accurate contact area determination. A new method is proposed for the determination of contact area based on residual imprint measurements using 3-D optical profilometry. The outcomes show that by measuring contact area with the new method the overall relative error in the obtained mechanical properties is improved. A combined Finite Element Analysis FEA and optimization algorithm has been developed using various indentation processes to determine the mechanical properties of a wide range of materials, using target FE indentation curves which were then extended to actual glass media taking into account the predicted residual stress in the material. The results obtained from the proposed methods of dual indenters and optimization algorithm have demonstrated that excellent convergence can be achieved with the target FE indentation curve of complex material systems; and also accurate results have been obtained for the actual glass. The material characterization tests were extended to investigate the fracture toughness based on the stress fields mapped at the unloading stage of the Vickers indentation. The median and Palmqvist crack systems were analysed separately using FEA. Dimensionless analyses were then carried out, and the critical SIF (fracture toughness) derived for the measured crack length and material properties. The developed numerical models were validated with the experimental data proposed by many researchers over a wide range of material properties as well as Vickers indentation induced cracking of thermally treated glass. The performance programme was designed as a comparative study with a range of conventional media that included an industrial benchmark media. Performance indicators included surface roughness and brightness. The results of the laboratory based research studies provided promising evidence that the thermally treated glass media has a process capability and performance comparable to that of conventional media. The glass media was trailed on a production machine annexed for this purpose. Turbine blades were employed as the component for these trails. The results though very promising did identify that a heavy workpiece may crush some media thereby generating small shards that may scratch or impair a fine surface finish (contribute against Ra). However, a novel jig arrangement was designed to hold the part in a horizontal position and allowed free rotation of the workpiece with the media flow in the trough. The new system was successfully used to deliver better performance results with the conventional and thermally treated recycled glass media. The kinematics of the mass finishing process were investigated with a two-dimensional discrete element model (DEM) developed to perform single-cell circulation in a vibratory bed. The sensitivity of the predicted model corresponding to the contact parameters was considered and the parameters were optimized with respect to the experimental results of media velocity vectors using particle image velocimetry (PIVLab). The results suggested that the bulk circulation increases with increasing bed depth resulting in an increase in pressure and shear forces between particle layers. The optimization of the advanced mass finishing (Drag and Stream finishing process) process has been studied using the design and analysis of experiment (DOE) approach. Regression analyses, analysis of variance (ANOVA), Taguchi methodology and Response Surface Methodology (RSM) have been chosen to aid this study. The effects of various finishing parameters were evaluated and the optimal parameters and conditions determined. The interaction of finishing parameters was established to illustrate the essential relationship between process parameters and surface roughness. The predicted models were confirmed by experimental validation and confirmation finishing trials

Experimental investigation of microstructure and properties in structural alloys through image analyses and multiresolution indentation

This work addresses the challenges in the investigation of structural alloy microstructures and their mechanical properties at multiple length scales. The investigations are performed on small volume ferrite-pearlite steel samples that were excised from in-service gas turbine components after prolonged exposure (up to 99,000 hours) to elevated temperatures, which promotes microstructural changes (spheroidization of pearlite and graphitization) as well as their yield strengths. Recent advances in spherical indentation protocols are combined for the first time to investigate the mechanical response of microscale ferrite-pearlite constituents and estimates of bulk properties on macroscale. It is shown that indentation yield strength captured with large indenter tips on an ensemble of ferrite-pearlite grains correlate strongly to the bulk yield strength evaluated with tensile measurements. Measurements on the individual ferrite and pearlite constituents follow a similar trend of decreasing yield strength as the bulk measurements. Second, to advance the reliability and accuracy of microstructure characterization, an image segmentation framework is developed that consists of five main steps designed to achieve systematic image segmentation on broad classes of microstructures utilizing widely available image processing tools. The flexibility and modularity of the framework was demonstrated on various types of microstructures images. The developed framework was used to segment the microstructures of ferrite-pearlite samples. The extracted microstructure statistics from the segmented images and multiresolution indentation yield strength measurements were used to evaluate established composite theory estimates and have demonstrated highly consistent estimates for these material systems.Ph.D

Mechanical Properties of La0.6Sr0.4Co0.2Fe0.8O3 Fuel Cell Electrodes

Mixed ionic-electronic conductive (MIEC) perovskite material La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF6428) is a promising candidate for the cathode in intermediate temperature solid oxide fuel cells (IT-SOFCs). Understanding the three dimensional (3D) microstructural characteristics of such a material is crucial to its application because they predominately determine the performance and durability of the porous cathodes and hence of the SOFCs. They affect the overall cathode kinetics and thus the electrochemical reaction efficiency, as well as the mechanical properties, which dominate the lifetime of SOFCs. It is necessary to balance the trade-off between the electrochemical performance, which is improved by high porosity and minimal sintering, and the ability to withstand mechanical constraints, which is improved by the opposite. To date LSCF6428 has been widely investigated on subjects of microstructure-related electrochemical performance, while little work has been reported on the mechanical properties and their correlation with the 3D microstructures. The main purpose of this research was to study the mechanical properties (i.e. elastic modulus, hardness and fracture toughness) of LSCF6428 cathode films and bulk samples fabricated by high temperature sintering, and to evaluate the effect of 3D microstructural parameters on elastic modulus, and the Poisson’s ratio where applicable, by means of both experimental and numerical methods. Room-temperature mechanical properties were investigated by nanoindentation of porous bulk samples and porous films sintered at temperatures from 900 to 1200 °C. A spherical indenter was used so that the contact area was much greater than the scale of the porous microstructure. The elastic modulus of the bulk samples was found to increase from 33.8 to 174.3 GPa and hardness from 0.64 to 5.32 GPa as the porosity decreased from 45 to 5 vol% after sintering at 900 to 1200 °C. Densification under the indenter was found to have little influence on the measured elastic modulus. The residual porosity in the nominally dense sample was found to account for the discrepancy between the elastic moduli measured by nanoindentation and by impulse excitation. Based on the optimisation of a commercial LSCF6428 ink formulation, crack-free films of acceptable surface roughness for indentation were also prepared by sintering at 900 to 1200 °C. It was shown that reliable measurements of the true properties of the films were obtained by data extrapolation provided that the effects from both surface roughness and substrate were minimised to neglected levels within a certain range of indentation depth to film thickness ratio (which was 0.1 to 0.2 in this study).The elastic moduli of the films and bulk materials were approximately equal for a given porosity. Based on the crack length measurements for Berkovich-indented samples, the fracture toughnesses of bulk LSCF6428 were determined to increase from 0.51 to 0.99 MPa·m1/2, after sintering at 900 to 1200 °C. The microstructures of films before and after indentation were characterised using FIB/SEM slice and view technique and the actual 3D microstructure models of the porous films were reconstructed based on the tomographic data obtained. Finite element modelling of the elastic modulus of the resulting microstructures showed excellent agreement with the nanoindentation results. The 3D microstructures were numerically modified at constant porosity by applying a cellular automaton algorithm based method, so that the influence on elastic modulus of factors other than porosity could be evaluated. It was found that the heterogeneity of the pore structure has a significant influence on the elastic properties computed using mechanical simulation.Open Acces

Extraction of Superelastic Parameter Values from Instrumented Indentation Data

Interest in superelastic (and shape memory) materials continues to rise, and there is a strong incentive to develop techniques for monitoring of their superelastic characteristics. This is conventionally done via uniaxial testing, but there are many advantages to having a capability for obtaining these characteristics (in the form of parameter values in a constitutive law) via indentation testing. Specimens can then be small, require minimal preparation and be obtainable from components in service. Interrogation of small volumes also allows mapping of properties over a surface. On the other hand, the tested volume must be large enough for its response to be representative of behaviour. Precisely the same arguments apply to more “mainstream” mechanical properties, such as yielding and work hardening characteristics. Indeed, there has been considerable progress in that area recently, using FEM simulation to predict indentation outcomes, evaluating the “goodness of fit” for particular sets of parameter values and converging on a best-fit combination. A similar approach can be used to obtain superelastic parameters, but little work has been done hitherto on sensitivities, uniqueness characteristics or optimal methodologies and the procedures are complicated by limitations to the constitutive laws in current use. The current work presents a comprehensive examination of the issues involved, using experimental (uniaxial and indentation) data for a NiTi Shape Memory Alloy. It was found that it is possible to obtain the superelastic parameter values using a single indenter shape (spherical). Information is also presented on sensitivities and the probable reliability of such parameters obtained in this way for an unknown material.National Council for Scientific and Technological Development (CNPq) - Brazi

Nanoindentation testing of soft polymers : computation, experiments and parameters identification

Since nanoindentation technique is able to measure the mechanical properties of extremely thin layers and small volumes with high resolution, it also became one of the important testing techniques for thin polymer layers and coatings. This dissertation is focusing on the characterization of polymers using nanoindentation, which is dealt with numerical computation, experiments and parameters identification. An analysis procedure is developed with the FEM based inverse method to evaluate the hyperelasticity and time-dependent properties. This procedure is firstly verified with a parameters re-identification concept. An important issue in this dissertation is to take the error contributions in real nanoindentation experiments into account. Therefore, the effects of surface roughness, adhesion force, friction and the real shape of the tip are involved in the numerical model to minimize the systematic error between the experimental responses and the numerical predictions. The effects are quantified as functions or models with corresponding parameters to be identified. Finally, data from uniaxial or biaxial tensile tests and macroindentation tests are taken into account. The comparison of these different loading situations provides a validation of the proposed material model and a deep insight into nanoindentation of polymers.Da Nanoindentation die Messung der mechanischen Eigenschaften von dünnen Schichten und kleinen Volumen mit hoher Auflösung ermöglicht, hat sich diese Messmethode zu einer der wichtigsten Testmethoden für dünne Polymerschichten und -beschichtungen entwickelt. Diese Dissertation konzentriert sich auf die Charakterisierung von Polymeren mittels Nanoindentation, die in Form von numerischen Berechnungen, Experimenten und Parameteridentifikationen behandelt wird. Es wurde ein Auswertungsverfahren mit einer FEM basierten inversen Methode zur Berechnung der Hyperelastizität und der zeitabhängigen Eigenschaften entwickelt. Dieses Verfahren wird zunächst mit einem Konzept der Parameter Re-Identifikation verifiziert. Fehlerquellen wie Oberflächenrauheit, Adhäsionskräfte, Reibung und die tatsächlichen Form der Indenterspitze werden in das numerische Modell eingebunden, um die Abweichungen der numerischen Vorhersagen von den experimentellen Ergebnissen zu minimieren. Diese Einflüsse werden als Funktionen oder Modelle mit dazugehörigen, zu identifizierenden Parametern, quantifiziert. Abschließend werden Messwerte aus uni- oder biaxialen Zugversuchen und Makroindentationsversuchen betrachtet. Der Vergleich dieser verschiedenen Belastungszustände liefert eine Bestätigung des vorgeschlagenen Materialmodells und verschafft einen tieferen Einblick in die bei der Nanoindentation von Polymeren ablaufenden Mechanismen

A holistic inverse approach on depth-sensing indentation characterisation and its application for predicting residual stresses in multi-phase inertia friction welds

The present study is concerned with the development of an inverse analysis of the depth-sensing indentation test based on a multi-objective function (MOF) optimisation model. The input data of this model are the load-displacement (P-h) curve extracted from the indentation instrument and the surface topography of the residual imprint left by the indenter after the removal of the load measured via atomic force microscopy (AFM). A Swift’s power law material model was considered to represent the indented material and thus, the output of the optimisation are the Young’s modulus (E), yield stress (σy) and strain-hardening exponent (n). The optimisation problem was designed to minimise the error between both the experimental and predicted P-h curves, i.e. the first objective, and pile-up profiles, i.e. the second objective, with the aim of addressing the non-uniqueness of the inverse analysis of indentation. A 3D FE model of the depth-sensing indentation test has been developed in ABAQUS in order to generate the predicted data from a set of trial material properties, i.e. E, σy and n. The generation of FE input files (pre-processor) and extraction of FE output files (post-processor) have been automated through MATLAB and Python subroutines. The optimisation problem was solved by the trust-region reflective algorithm available in the MATLAB Optimization ToolboxTM and thus, concisely, the model minimised the experimental and predicted data by modifying iteratively the material properties, starting from the initial guess properties specified by the user, until convergence was reached. Upon convergence, the material properties were said to describe the elastic-plastic behaviour of the indented material. A comprehensive experimental programme was carried out in order to investigate the load dependency of the indentation response of three different materials, including a steel (CrMoV), a titanium alloy (Ti-6Al-4V) and a high-purity copper (C110). The study of the topography of the residual imprints provided a better understanding of the effects of the microstructural arrangement on the plastic displacement of material beneath the indenter. The extent of piling-up was observed to be very sensitive to the difference in material properties from grain to grain and the crystallographic plane of the indented grain. Furthermore, it was concluded that the structural arrangement of the indented material may also contribute to the asymmetry observed in the pile-up profiles, in particular in materials with large grains relative to the projected area of the indenter, e.g. C110. This piece of work therefore, is suggested as a guideline for the use of height measurements of the residual imprint in the characterisation of the plastic behaviour of materials. The multi-objective function optimisation model is proved to be a step forward to the characterisation of the near-surface properties as, in contrast to the P-h curve, the residual imprint is strongly linked to the plastic behaviour of the indented material. Therefore, the physics governing the indentation problem were better represented. Therefore, the optimised P-h curve provided a very good fit to the corresponding experimental curve, to within an error of less than 2.4% and 8.4% the maximum (hmax) and residual (hr) depth, respectively, for all three materials, CrMoV steel, C110 copper and Ti-6Al-4V. Furthermore, a deviation of less than 12.4% was achieved between the area of indentation provided by the FE model and AFM instrument. Additionally, the value of maximum peak height (hpeak) was predicted with a maximum error of 11% in relation with the experimental pile-up profiles. Therefore, it was concluded that the optimised solution provided a very good representation of the complex mechanical response to indentation such that the volume of plastically displaced material as predicted by the optimised FE model was observed notably in accordance with experimental measurements. Furthermore, the complementary information provided by the second objective function allowed the model to distinguish between different materials showing identical indentation response – referred to in the literature as ‘mystical’ materials. In addition, a key outcome of this investigation suggested that stress-strain curves generated by mechanical tests performed at different scales, exhibit similar behaviour with only the magnitude of the stress increasing or decreasing depending upon the scale. Part of this thesis is dedicated to the application of the proposed inverse analysis for the characterisation of three phases located across the joint of a like-to-like inertia friction weld of SCMV steel, including martensite in the tempered, quenched and over-tempered condition. This study, characterised the generation of residual stresses into two stages: the thermal strain dominated initial cooling period that accounts for the majority of the residual stresses, and the phase transformation strain dominated final cooling period. In addition, it was concluded that at the onset of transformation from austenite to martensite, the volumetric changes experienced in the lattice relax up to 70% of the predicted tensile hoop stress found in the vicinity of the weld line near the inner surface and that the interaction of soft regions of austenite and hard regions of heat unaffected martensite accounts for up to 17% of the peak tensile stress. The indentation response of the set of optimised properties that represent each of the phases, was in very good agreement with the corresponding P-h curve and residual pile-up profile extracted from the indentation instrument and AFM, respectively. The capability of the inverse analysis to build the stress-strain relationship in the elastic-plastic regime using the optimised mechanical properties of the parent metal has been validated using experimental data extracted from the compressive test of an axisymmetric sample of tempered martensite [1]. The inclusion of the softer over-tempered martensite phase allowed the FE prediction to determine the proportion of the heat affected zone (HAZ) comprised by each phase in better agreement with the experimental weld-trial. Based on the interpretation of the microhardness test performed across the weld, the harder region formed due to the quenching process extends approximately 54% the length of the HAZ, whereas the rest 46% is comprised by the softer over-tempered martensitic phase. According to the FE prediction, the heat affected zone was composed by a proportion of 57% quenched martensite and 43% over-tempered martensite. Moreover, the distance from the weld line to the region where martensite fully tempered was observed to extend 79 and 71% the length of the HAZ, as determined by the FE model and experimental measurements, respectively. The presence of a softer region, OTM, between two harder regions, namely QM and TM, relaxed 7 to 11%, 1 to 6% and 12.8 to 15.3% the peak values of stress in the radial, axial and hoop directions respectively. A key observation from the results of the FE prediction was that the peak hoop residual stress is located at the boundary of the quenched and over-tempered martensite, and not at the edge of the heat affected zone. This observation was in agreement with the residual stress measurements published by Moat et al. [2]

Structure and mechanical properties of aluminosilicate glasses

The effect of phosphate on the mechanical properties of aluminosilicate glasses so far has barely been studied. Yet, phosphate incorporation bears potential for changing the polymerisation of aluminosilicate glasses and thus their properties. This thesis presents the first detailed mechanical analysis of phospho-aluminosilicate glasses that includes elastic properties. The studied compositions comprised metaluminous glasses from the system SiO2 - Al2O3 - Na2O - P2O5 with 0 to 7.5 mol% P2O5 and 50 to 70 mol% SiO2. The glass hardness and elastic properties were assessed by several techniques of indentation and sound speed measurement and were found to decrease with increasing P2O5 content. Changes of these properties with increasing SiO2 content were less expressed and could be explained by either density changes or polymerisation. Additionally, the densification upon indentation was studied, as well as crack resistance and strain rate sensitivity. Furthermore, phosphate was found to decrease the glass transition temperature and to impede crystallisation. To tailor glass properties, the structure-property relationships need to be understood. This thesis includes a structural analysis by combined infrared and Raman spectroscopy. A far-infrared analysis of the sodium signal indicated a competition between aluminate and phosphate groups for charge-balancing sodium. Also, a correlation was found between shifts in infrared and Raman spectra and the degree of ionic bonding, represented by the theoretical optical basicity. In summary, the mechanical properties and the structure-property relationships of metaluminous phospho-aluminosilicate glasses were characterised and the analysis of the degree of ionic bonding and of the role of sodium provided new structural insights