Dynamic properties of soils (shear stiffness and damping ratio) are critical for the design of structures subjected to vibrations. The dynamic properties of a benchmark standardized laboratory sand (Ottawa silica sand) were evaluated with two different resonant column devices, utilising software with different analytical approaches for the evaluation of soil properties. The dynamic properties (shear modulus and damping ratio) are evaluated as a function of the shear strain level. The results are compared to evaluate the effect of the type of equipment and the form of the data analysis on the measured dynamic properties of the samples. The results are discussed in light of the applicability of the procedures in practice, the ease of the testing methods, and the errors they introduced into analysis and design. In general, the shear wave velocities obtained from the two different devices are in good agreement. However, the damping ratios they give show considerable differences as strains increase. Dynamic properties are typically measured by curve fitting of the transfer function between the excitation and the response using the resonant column device. However, the force function generated by sinusoidal sweep or random noise excitations induce different shear strain levels at different frequencies. Consequently, the shape of the measured transfer function is distorted and differs from the theoretical transfer function for an equivalent single-degree-of-freedom system. The difference between the measured and theoretical transfer functions as well as the bias in the computed dynamic properties becomes more pronounced with the increase in shear strain. This study presents a new methodology for the evaluation of dynamic properties from an equivalent constant-strain transfer function. The soil specimen is excited simultaneously using a sinusoidal excitation (carrier signal) at the required strain level and a small amplitude, narrow band random noise. The strain level induced by the fixed sine is shown to control the resonant frequency of the specimen; whereas the random noise introduces the required frequency bandwidth to determine the transfer function and hence the dynamic properties at a constant strain level. The new methodology also shows a good potential for the evaluation of frequency effects on the dynamic properties of soils in resonant column testing.

In this thesis, ferroelastic domain switching behaviour of lead zirconate titanate ceramics, as used in devices such as actuators, was studied. In particular, the effect of cyclic frequency and amplitude were assessed to develop a correlation between macrostructural changes and fatigue behaviour, both in the bulk and in crack-tip process zones. A variety of experimental methods were used. Raman scattering enabled the poling state of the ceramics can be determined. However, it could not distinguish between the different preferred orientations of in-plane c-domains. Conversely, neutron and X-ray diffraction technique can detect domain orientation distribution and the preferred direction of c-domains. In this study, neutron diffraction was used to probe domain switching behaviour in bulk samples while high spatial resolution X-rays were employed to analyse a switching zone near a crack tip. Under cyclic mechanical loading, domain switching and the accumulation of ferroelastic strain becomes saturated with increasing number of cycles. Moreover, time-dependent deformation was investigated. The results show that a domain forward-switching process occurs during creep deformation while a domain backward-switching process takes place during recovery. In addition, it was found that the frequency of applied stress affects the saturation of the ferroelastic strain while its magnitude has an influence on the level of strain accumulated. Under static mechanical loading, it was found that the size of the crack-tip zone where stress-induced domain switching occurs with increase in the stress intensity factor but the degree of domain switching around the crack tip changes only slightly. Under cyclic electrical loading, the results present a strong link between the frequency of the applied field, remnant polarisation, domain switching and the resultant crack growth. The results show that polarisation fatigue, the size of the switching zone, and the crack growth rate is greater at lower loading frequency. The quantitative analysis of the time dependent mechanism as well as the effect of loading frequency and amplitude on domain switching was achieved by applying viscoelastic models. Importantly, these models can be used to explain domain switching behaviour and domain wall movement under cyclic loading and link these processes to macroscopic deformation.

Thesis (Ph.D.)--University of Wollongong, 2004. / Typescript. Includes bibliographical references: leaf 215-219.

Fibrous filter materials are commonly adopted in a variety of industrial and domestic processes to remove fine particles. Filter performance may be assessed by two parameters: the proportion of particles passing through the media (penetration), and the resistance to gas flow through the filter (pressure drop). Another parameter, the filter lifetime, may be important where economical factors are key.

abstract: t temperature (HST) and top-oil temperature (TOT) are reliable indicators of the insulation temperature. The objective of this project is to use thermal models to estimate the transformer's maximum dynamic loading capacity without violating the HST and TOT thermal limits set by the operator. In order to ensure the optimal loading, the temperature predictions of the thermal models need to be accurate. A number of transformer thermal models are available in the literature. In present practice, the IEEE Clause 7 model is used by the industry to make these predictions. However, a linear regression based thermal model has been observed to be more accurate than the IEEE model. These two models have been studied in this work. This document presents the research conducted to discriminate between reliable and unreliable models with the help of certain metrics. This was done by first eyeballing the prediction performance and then evaluating a number of mathematical metrics. Efforts were made to recognize the cause behind an unreliable model. Also research was conducted to improve the accuracy of the performance of the existing models. A new application, described in this document, has been developed to automate the process of building thermal models for multiple transformers. These thermal models can then be used for transformer dynamic loading. / Dissertation/Thesis / Masters Thesis Engineering 2014

L'évaluation de la durée de vie en fatigue est essentielle dans la conception de structures. Sous estimé les prévisions peut entraîner des inspections en service inutiles. En revanche, les prévisions surestimées peuvent avoir des conséquences graves sur l'intégrité des structures.Dans certains composants de centrale nucléaire, un chargement mécanique en fatigue équi-biaxiale est décelé. L’identification de l'impact potentiel de chargement multiaxial sur la durée de vie des composants est une préoccupation majeure. Peu de données expérimentales sont disponibles sur les aciers inoxydables austénitiques présents au niveau des circuits REP. Il est ainsi essentiel d'améliorer les méthodes d'évaluation de la fatigue afin de prendre en compte les dommages potentiels de la fatigue équi-biaxiale. Par conséquent cela nécessite l'obtention de données expérimentales sur le matériau considéré avec une sollicitation mécanique équi-biaxiale.Le but de cette étude est de présenter les résultats expérimentaux et numériques obtenus avec un dispositif "FABIME2" développé au CEA/LISN en collaboration avec EDF et AREVA. L’association des résultats expérimentaux obtenus avec une analyse numérique, réalisée sur le code de calcul Cast3m,a permis de mettre en évidence l’effet aggravant d’un chargement équi-biaxial sur l’amorçage de fissure mais qui reste couvert par la courbe de conception définie par l’industrie nucléaire. Côté propagation de fissure, une première approche simplificatrice a permis d’étudier la cinétique d propagation de fissure en fatigue équi-biaxiale. / Fatigue lifetime assessment is essential in the design of structures. Under-estimated predictions mayresult in unnecessary in service inspections. Conversely, over-estimated predictions may have seriousconsequences on the integrity of structures.In some nuclear power plant components, the fatigue loading may be equi-biaxial because of thermalfatigue. So the potential impact of multiaxial loading on the fatigue life of components is a majorconcern. Meanwhile, few experimental data are available on austenitic stainless steels. It is essentialto improve the fatigue assessment methodologies to take into account the potential equi-biaxialfatigue damage. Hence this requires obtaining experimental data on the considered material with astrain tensor in equi-biaxial tension.The aim of this study is to present the experimental and numerical results obtained with a device"FABIME2" developed in the LISN in collaboration with EDF and AREVA. The association of theexperimental results, obtained on the new experimental fatigue device FABIME2, with the numericalanalyses obtained by FEM simulation with Cast3M code, has enabled to define the aggravating effectof the equibiaxial fatigue loading. However, this effect is covered by the Design fatigue curve definedfrom the nuclear industry. For the crack propagation, a first simplified approach enables to study thekinetic behavior of crack propagation in equibiaxial fatigue.

Components found within many industries contain crack like defects. The work detailed here considers such a component under the combined influence of primary and secondary stresses; where primary stresses contribute to plastic collapse and secondary stresses are redistributed under plastic deformation. A number of approaches are available to detail the combined loading on the crack tip parameter J, or KJ, which is used to assess proximity to failure from crack extension. However, these approaches are recognised to be conservative and can lead to the unnecessary replacement of components, stricter surveillance and inspection regulations, and further costs associated with downtime.The aim of the work presented is to investigate these conservatisms and develop a further approach to quantify the interaction of primary and secondary stresses on fracture. A large matrix of cracked body finite element analyses of a circumferentially cracked cylinder has been performed under a range of loadings. This is then used to detail the interaction of primary and secondary stresses on fracture by providing a function to describe a scaling term, g, that multiplies the secondary crack driving force contribution. This term has been shown to be relatively independent on the magnitude of secondary stresses and is also dependent on the material stress strain relation. This relation for g has also been shown to be compatible with the R6 defect assessment procedures V factor approach, through the Vg plasticity interaction term, that provides a scaling term to the secondary contribution in R6. A review of experiments considering combined loading has indicated that the number of tests that cover a range of primary stress induced plasticity levels is limited. Further experiments were therefore considered within this research to provide added experimental fracture toughness data by which to compare the R6 V factor and Vg approaches. These experiments introduced a compressive pre-load to the ends of three-point bend specimens so that a tensile residual stress resulted on unloading. A crack was introduced and the specimens tested at one of three temperatures so that changes in the materials fracture toughness with temperature ensured different levels of plasticity at failure; so that crack growth occurred over three sets of load normalised to the load for plastic collapse. Tests were also conducted that did not include the residual stress so that the effect of residual stress could be shown under different levels of plastic redistribution. The Vg Approach and the existing Complex R6 V Approach have then been applied to all available experimental data for validation. The results show that both approaches conservatively predict the failure of all tests and that the Vg Approach can reduce the level of conservatism.

Investment into offshore wind farms has been growing to address the growing threat of climate change. The majority of offshore wind turbines (both current and planned) are founded on monopiles, large circular steel pipe piles ranging from 4.0 m – 7.5 m in diameter. Based on available borehole records, most planned wind turbines in the UK will be founded in overconsolidated clay deposits. Monopile design is done via usage of the well established p-y curves. However, there are issues with the usage of the p-y curves. Firstly, the curves may be unsuitable to model the monopile’s behaviour as it is expected to behave similarly to a rigid pile rather than flexibly. Secondly, the curves may not accurately estimate the initial pile-soil stiffness. Thirdly, the curves are not comprehensive enough to account for the accumulated strain and stiffness changes resulting from cyclic loading. Considering these issues, research was carried out to improve the current design of monopiles in clay by carrying out displacement controlled monotonic and load controlled cyclic load tests in a centrifuge. Results from monotonic tests suggest that the DNV (2014) design methodology to construct p-y curves in clay based on Matlock’s (1970) soft clay criterion significantly underestimate stiffness. Findings suggested that the experimental p-y curves could be characterised through modification of the criterion. Modification of the criterion produced estimates that matched the 3.83 m monopile experimental curves. Pile toe shear force was observed to contribute little to ultimate lateral resistance and stiffness. Despite the marginal contribution, an effort was made to characterise the pile toe shear force. Estimates of the modified criterion on the 7.62 m monopile did not match the observations, indicating that further research should be carried out to improve the modified criterion. The cyclic tests displayed two distinct regimes; the stiffening regime and the softening regime. Results suggests that cyclic loads of different characteristics influence the locked in stress conditions of the soil which in turn influence the excess pore pressure behaviour, hence dictating whether the stiffening or softening regime takes place. Suggestions were made regarding the conditions that dictated whether the stiffening or softening regime would take place. In the stiffening regime, the stiffening rate decreased with increasing strain while as the accumulated rotation rate increased with vertical load for the same cyclic load magnitude. The softening regime was determined to be extremely detrimental as the high rates of softening and accumulated rotations could cause failure of the system in the short-term. Recommendations were made to estimate the cyclic stiffness and accumulated rotations resulting from both stiffening and softening regime.

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