Within the aerospace industry, the reduction of costs associated with operation, manufacture and development of gas turbine engines is a primary objective. Component and assembly design optimisations can satisfy weight reductions which correspond to operational and manufacturing cost reductions. Development cost can be reduced by implementing additional numerical validation stages as an alternative to experimental validation alone. Therefore, the overarching purpose of this research is the development of a computationally efficient constitutive modelling tool, which predicts the macroscopic deformation and failure of fan system components and assemblies during dynamic and highly non-linear thermo-mechanical loading. At the macroscopic scale a series of physical deformation and failure phenomena have been identified from the literature which are necessary for accurate representation of the dynamic behaviour of Ti-6Al-4V. Across the surveyed literature these capabilities have not been implemented together within a single constitutive framework prior to the commencement of this research. Experimental support provides validation data for the subsequent constitutive modelling activities, whilst also demonstrating the importance of strain-rate sensitivity, tension-compression asymmetry and anisotropic behaviour associated with texture orientation in Ti-6Al-4V. Numerical studies were also conducted to develop a robust procedure for rapid assimilation of uni-axial experimental data within constitutive benchmarking models, for development purposes. Further parametric studies of sub-component plate impact benchmarks revealed several limitations within the commercially available solutions. These limitations are related to mesh sensitivity and damage evolution. A technique has been proposed which couples damage evolution and imposes a directional length-scale. This provides enhanced mesh insensitivity and damage evolution rate control. However, a single damage evolution mechanism was demonstrated to be insufficient when representing shear damage mechanisms in uni-axial and multi-axial loading regimes. Therefore, an additional damage mechanism has been developed and coupled with the mesh sensitivity and localisation technique. The resulting cumulative and competitive damage evolution and localisation capabilities reflect the localisation characteristics observed in the literature. The variability of alloy manufacture and the subsequent macroscopically observed behaviour remain a limitation within an isotropic framework. This has motivated the development of both asymmetric and anisotropic formulations, integrated within the newly proposed multi-mode damage localisation framework. The ability of the newly implemented non-isotropic framework successfully provides both asymmetric yielding and hardening capabilities and anisotropic evolution. These developments have been demonstrated against experimentally obtained results for validation and calibration purposes. Together these capabilities allow for accurate representation of a wide range of macroscopically observable phenomena based upon micro mechanical mechanisms.

A visco-elastic-plastic mathematical model developed at Sheffield City Polytechnic was used to calculate the thermal stress and strain generated during the quenching of an infinite plate of high hardenability steel (835M30) in water, nine experimental oils and a polymer. In.the case of water, previous comparisons between experimental and calculated residual strains was poor. This discrepancy, during the present investigation, was reduced by introducing into the model the relationship between actual surface temperature and surface heat transfer coefficients and by incorporating the effects of various surface finishes into the model. However this discrepancy still remains to a limited extent. The same mathematical model was used to investigate the quenching characteristics of a number of experimental oils: overall the calculatedresidual stresses and strains compared well with the corresponding experimental data. The experimental oilscontained mixtures of additives. Those based on sodiumsulphonate increased the rate of cooling during quenching and the associated absolute residual stresses at a fixed point in the plate. Simultaneously the residual strains were reduced. The use of the succinimide additive produced converse effects in each case. The investigation also included the quenching of plates in polymer solutions of varying concentrations to provide a basis for comparison between the three most commonly used quenchants, viz. water, oil and water soluble polymers. The results indicated that in terms of the residual stresses and strains the oils produced smaller values particularly in the latter case when compared with the polymers. However when compared with water both the oils and water soluble polymers produced significantly smaller residual stresses and strains. The quenching characteristics were also investigated by the use of photography which gave an insight into the cooling characteristics of each quenchant. A water quench produced masses of fine bubbles during the nucleate boiling stage whilst this stage was characterised by large vapour blisters moving up the face of the plate in the case of the experimental oils. Previous photographic evidence indicated that solid polymer was deposited during quench and coated the plate with a gel-like substance which returned back into solution when the temperature was low enough.

The aim of this work was to visualise heterogeneous deformation in snow under controlled laboratory conditions. Heterogeneous deformation was observed for both homogenous and heterogeneous loading conditions. Understanding deformation of snow is important in many scientific fields including vehicle traction, avalanche forecasting, and winter sports. This thesis investigates the deformation behaviour of snow on the centimetre scale under moderate strain rates (0.005 to 0.1 s-1) when subject to one-dimensional compression or to indentation. In order to allow controlled and repeatable snow deformation experiments, a new type of artificial snow was developed. This snow type was examined by low temperature scanning electron microscopy and by traditional avalanche observer’s methodology. Penetrometer experiments were conducted on the artificial snow and on natural seasonal snow in Scotland. The two snow types were found to be similar: results obtained on artificial snow are thus applicable to natural snow. A reproducible technique of manufacture and a thorough characterisation of the artificial snow are presented. One-dimensional compression experiments were conducted on the artificial snow. The experiments were in confined compression in a specially constructed apparatus, designed to provide for back-lit photography. Images were taken at 0.25 second intervals and analysed using digital image correlation, thus providing 2D strain fields. With careful control of photographic parameters, it is demonstrated that process of applying tracer substances to the snow is not necessary, thus allowing an unprecedented resolution. Spontaneously-forming strain localisations were observed for the first time, indicating strain softening behaviour. Damage was observed to propagate through the specimen as a moving front, resembling a wave. The force required to propagate the front remained nearly constant until the whole specimen was compacted, at which point a new front formed and the process repeated. The experimental method was extended to 2D indention experiments with a range of sizes and shapes of indenter. Complex deformation fields were observed, extending up to 6 times the width of the indenter on each side. Observed deformation included tensile tearing as well as compression and shear. The maximum local strain achieved in the indentation experiments was similar to that achieved by the first compaction front in one-dimensional compression. The work here presented has implications for snow deformation generally: strain localisation introduces a characteristic length, which may prevent scaling of models or results. The indentation results are particularly relevant to snow penetrometry, where indentation experiments are used to try and extract microstructural information from buried snow layers for the purpose of avalanche prediction. The common assumption that the penetrometer interacts only with snow very close to its tip may need to be reconsidered.

PURPOSE. The purpose of this study was to quantify the biomechanical response of human posterior ocular tissues from donors of various racioethnic groups to better understand how differences in these properties may play a role in the racioethnic health disparities known to exist in glaucoma. METHODS. Sequential digital image correlation (S-DIC) was used to measure the pressure-induced surface deformations of 23 normal human posterior poles from three racioethnic groups: African descent (AD), European descent (ED), and Hispanic ethnicity (HIS). Regional in-plane principal strains were compared across three zones: the optic nerve stump (ONS), the peripapillary (PP) sclera, and non-PP sclera. RESULTS. The PP scleral tensile strains were found to be lower for ED eyes compared with AD and HIS eyes at 15 mm Hg (P = 0.024 and 0.039, respectively). The mean compressive strains were significantly higher for AD eyes compared with ED eyes at 15 mm Hg (P = 0.018). We also found that the relationship between tensile strain and pressure was significant for those of ED and HIS eyes (P < 0.001 and P = 0.004, respectively), whereas it was not significant for those of AD (P = 0.392). CONCLUSIONS. Our results suggest that, assuming glaucomatous nerve loss is caused by mechanical strains in the vicinity of the optic nerve head, the mechanism of increased glaucoma prevalence may be different in those of AD versus HIS. Our ONS strain analysis also suggested that it may be important to account for ONS geometry and material properties in future scleral biomechanical analysis.

The stress-strain behaviour of granular soils under monotonic and cyclic loading conditions and small lateral strains was studied in this work. A simple cubic triaxial apparatus (SCTA), originally developed at Leeds University for monotonic stress-strain studies of sand under controlled and small lateral strains, was used in this investigation. The three principal stresses and strains can be independentLy controlled and measured in this apparatus. The SCTA was modified and further developed to allow cyclic stress-strain studies of granular soils-to be performed. To increase the stress-strain data available on granular soils similar tests to those previously carried out on the medium sand, were performed on fine and coarse sands under monotonic loading conditions. The samples tested were cubic of 150 mm side length and prepared with ranges of initial porosities in a dry condition. To study the cyclic stress-strain behaviour of sand at small strains, a series of new tests on similar cubic samples of the medium sand were performed under cyclic loading conditions. Cyclic loads with different frequencies, amplitudes and number of cycles were applied and the samples were prepared dry at the loosest and densest conditions. Values of the coefficients of active pressure, earth pressure at rest, constrained secant modulus, Young's modulus and Poisson's ratio for the fine, medium and coarse sands were obtained and compared for different conditions. The relationships between vertical and lateral stresses are found and the volume change behaviour of sands in different conditions are studied. Finally some comparisons are made between the results obtained from monotonic and cyclic loading conditions.

The Bella Coola area geographically straddles two zones of known Early to mid-Cretaceous sinistral ductile strain; the Grenville, Kitkatla, and Principe-Laredo shear zones to the northwest located near Prince Rupert, B.C., and the Tchaikazan fault system to the southeast. At the latitude of Bella Coola in west-central B.C., the Pootlass High Strain Zone (PHSZ) is a ductile, subvertical, shear zone system at least 2 km wide and at least 30 km long. The purpose of this study is to determine the age, kinematics, and tectonic significance of the PHSZ, and to investigate whether or not it was active as a kinematic link to Early to mid-Cretaceous sinistral ductile strain zones in the western Canadian Cordillera. This thesis reports recent observations from field mapping and new geochronological, microstructural, and petrological data, from which the PHSZ is characterized and placed into a regional tectonic framework. U-Pb and 40Ar/39Ar isotopic geochronology indicate that regionally extensive, southwest-vergent folding in the PHSZ area was active prior to 114 Ma and persisted until at least 73 Ma. High-temperature, ductile, sinistral non-coaxial strain in the PHSZ was accommodated between 76 (or earlier) and 62 Ma. Localization of high strain is associated with the emplacement of plutonic rock and abundant intrusive sills, which likely acted as a strain-softening mechanism. L-tectonites within the deformed plutonic rocks attest to the weakness of the rocks during deformation and support syn-kinematic magmatism. Geothermometric and petrological data suggest that deformation occurred at temperatures of 537 to 731°C and at crustal depths of —23 km. The PHSZ is interpreted to be kinematically related to the Talchako Fault to the east, which was active as a sinistral mylonitic shear zone between 70 and 65 Ma. A kinematic relationship between the PHSZ and the Grenville, Kitkatla and Principe-Laredo shear zones near Prince Rupert imply a protracted history of sinistral transpression in the Coast Mountains of British Columbia that persisted in the Bella Coola region through Late Cretaceous time. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

No description available.

M.Phil. / In today's world with its competitive environment there is a need to shorten product development time by using CFD (Computational Fluid Dynamics) to design an object for example a car, aeroplane or missile and to predict the forces that the wind will have on the object (design). To evaluate the correctness of the CFD results, the design or a scale model of the design must be tested in a wind tunnel by using a force balance. The wind tunnel balance is an apparatus used in the designing and testing of wings, shapes and profiles. In general a balance can be used in all aerodynamic designs to determine the forces on an object when it is moving through air. The aim of this project was to design and manufacture a three-component external balance for a low-speed wind tunnel using an axiomatic design method. It also covers the installation of the external wind tunnel balance to a wind tunnel with a computerized data acquisition capturing system, and performance evaluation of the wind tunnel balance.

In this work, beneficial effects of tensile mean strain on fatigue behavior and microstructure of superelastic NiTi (i.e. Nitinol) are studied. Most applications, such as endovascular stents made with NiTi, are subjected to a combination of constant and cyclic loading; thus, understanding the fatigue behavior of NiTi undergoing mean strain loading is necessary. Cyclic strain-controlled fatigue tests are designed to investigate the effects of tensile mean strain on fatigue of superelastic NiTi. Experimental observations show that combinations of large tensile mean strains and small strain amplitudes improve the fatigue life of superelastic NiTi. This behavior arises from reversible, stress-induced phase transformations. The phase transformations cause “stress plateaus” or strain ranges with no change in stress value. Scanning electron microscopy (SEM) of the fracture surfaces of specimens revealed generally short crack growth. Electron backscatter diffraction (EBSD) found the amount of residual martensite to be about ~8%, regardless of loading conditions

Robert Agnew’s (1992) General Strain Theory significantly revitalized traditional scholarship in the anomie/strain tradition by offering a general theory of crime; purported to account for both criminal and analogous behaviors. GST specifically extends anomie/strain theory by introducing new sources of strain (i.e. loss of positively valued stimuli, presentation of noxious stimuli) into the theoretical framework, as well as elucidating the causal pathways (including mediating and moderating effects) leading from the experience of strain to deviant coping mechanisms. An emerging trend within GST is the identification of previously untapped sources of strain (e.g. victimization, discrimination) that ostensibly have deviancegenerating properties. Concerning the latter trend, recent empirical iterations of GST have also introduced internal (e.g. self-esteem) and external conditioning factors (e.g. social control) that have been found to exert a mediating effect on the relationship between strain-generated negative emotions and deviant coping responses. Jang and Johnson-in a recent series of studies (2003, 2005)-offered a crucial extension to the General Strain Theory (GST) literature by finding that religiosity at least partially moderates the deviance-generating effects of strain-induced negative affect among a sample of African Americans. The current study offers a key extension to the Jang and Johnson thesis by offering the most comprehensive examination of the central tenets of their research to a nationally-representative, longitudinal sample of adolescents. Results from Waves I and II of the National Longitudinal Study of Adolescent Health reveal support for GST in general, and qualified support for the Jang/Johnson thesis in particular. Strain was found to be a significant, positive predictor of depression and anger. With regard to the fundamental hypothesis of the current research, partial support was garnered for the Jang and Johnson hypothesis. In particular, religiosity only offered direct protective effects when predicting drug use, and failed to condition the relationship of strain on deviance across any of the deviance measures. Consequently, religiosity failed to moderate the effects of strain on deviant coping strategies among the full sample, although significant conditioning effects were observed for female deviance. Consequently, these results largely attribute the Jang and Johnson findings to elevated levels of religiosity in their sample.