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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Three dimensional finite element analysis of pile groups and piled-rafts

Wang, A. January 1996 (has links)
No description available.
32

Stress corrosion cracking in duplex stainless steels

Mohammed, Farej Ahmed January 2003 (has links)
No description available.
33

Study of the deformation of single-walled carbon nanotube(SWNT)/epoxy composites using Raman spectroscopy

Kao, Chih-chuan January 2008 (has links)
No description available.
34

Response Prediction and Detection in Non-linear Clamped Panels

Acton, Matthew Nicholas Frederick January 2008 (has links)
Aircraft panels may often be subjected to high levels ofacoustic pressure loading in flight that may lead to fatigue damage. In some cases, the in-plane restraint provided by the panel boundaries will introduce a geometric stiffening non-linearity when the panel deforms. This Thesis is split into two main areas in the field of non-linear dynamics. Firstly the prediction ofthe non-linear response ofa structure to acoustic excitation for use in sonic fatigue life calculations is examined. The second area of consideration is the detection ofthe presence of non-linearities in a structure when there may more than one present. The Non-Linear Modal method (NLMOD) previously developed at the University of Manchester, allows the prediction ofthe kinematic and stress response of such panels via a reduced order approach that converts Finite Element results into a model based in linear modal space, with additional terms included to represent the non-linear behavior. In this Thesis, the development ofan experimental clamped panel structure is presented, together with several Finite Element models ofthe same structure. The panel is tested for its modal and static characteristics and exposed to fairly high-level acoustic excitation in a Progressive Wave Tube (PWT). The resulting non-linear strain responses are compared to those predicted using the identified non-linear modal model. Discrepancies are initially found between test and prediction. Reasons for the discrepancies are discussed and the model modified accordingly. Good final agreement with test results is found and a number of areas for further investigation are highlighted. The second part of the Thesis develops a novel, simple method for detecting the presence of non-linear stiffness and non-linear damping, when both may be present, using higher order statistics ofthe time domain response ofa structure. The method is developed using simulation of a single degree offreedom system and is then validated using a clamped panel. In order to ensure the presence of non-linear damping, a novel discrete, non-linear damper is developed making use of a passive shaker with the terminals shorted.
35

Crack propagation in nuclear graphite

Hodgkins, Andrew D. January 2006 (has links)
No description available.
36

Failure analysis and performance modelling of a MEMS flexure electrothermal actuator

Lavu, Srikanth January 2008 (has links)
Reliability is a major challenge for the successful exploitation of MEMS technology. ' This thesis presents a systematic taxonomy of typical failure modes and effects in MEMS. The failures are classified according to their occurrence: manufacturing, operation, environmental effect and package related effect. To prioritise these failures, a systematic proactive Failure Mode and Effect Analysis (FMEA) is presented as a tool to be used concurrently in the design phase. The FMEA is successfully applied on a MEMS flexure electrothermal actuator. The FMEA study identified the key issues affecting the reliability of the considered actuators and provided val,uable recommendations to improve their functional performance, efficiency and reliability. Particular emphasis is put on the failure modes of the micro electrothermal flexure actuator and the corresponding failure mechanisms are presented. A high-level functional behavioural modelling methodology for fast and flexible modelling of multiphysical MEMS functional behaviour is presented using the VHDL-AMS language. In particular a high level behavioural model is described for the functional displacement of the electrothermal flexure actuator. Moreover, using the same approach a theoretical study of the performance is presented in the case of the electrothermal flexure actuator at low pressure and high temperature ambient conditions. Practical testing of the effects of low ambient pressures and high ambient temperatures on the performance and reliability of the thermal actuators has been performed. The test results are compared successfully with the results of the thermal actuators high level performance model to assess the validity and accuracy ofthe models.
37

On-line determination of component quality using acoustic emission

Ward, Charles January 2011 (has links)
No description available.
38

Haptic sensing technology for MEMS design and manufacture

Calis, Mustafa January 2008 (has links)
This thesis presents a design methodology for MEMS that integrates Cosserat theory into haptic sensing tec1mology. The Cosserat method is applied to the modelling of MEMS in an effort to reduce the complexity of the modelling and to provide a more accurate representation of stress in miniaturised devices. The approach developed uses a new semi-analytical technique based on both power series expansion and a multimodal approximate method. To demonstrate the feasibility of the proposed model, our method is tested successfully with simple MEMS components and compared with FEM and analytical solutions. Simple MEMS structures are implemented in a haptic environment to check the feasibility of real-time simulation using this theory. A userfriendly interface is also developed that allows the real-time display of simple MEMS structures such as a cantilever microbeam, a microbridge and a plate undergoing loads and the corresponding bending with force-feedback rendering and quantitative deflections. None of the existing CAD software packages for Microsystems enable real-time displays of accurate deflections.. Novel haptic implementations of surface interactions, such as the Casimir effect, are also implemented which have the potential to guide designers during the assembly process or to train engineers/scientists.
39

The influence of mineralogy and microstructure on the contaminant migration through geosynthetic clay liners

McLoughlin, Michael January 2004 (has links)
This thesis is concerned with the current contentious issue of environmental containment. This work provides an assessment of contaminant migration through Geosynthetic Clay Liners (GCLs). GCLs are thin liners usually consisting of three layers, defined in section 2.2.4. These are factory manufactured materials, used extensively in the waterproofing and environmental containment markets. The predominant, if not the only "low flow" element in GCLs is bentonite, described in section 2.4.1. Bentonite has been found to be most advantageous as the waterproofing core of GCLs. During this research, emphasis was placed on an investigation as to the nature of the low flow core of the GCLs in terms of mineralogy and microstructure. GCL types can be divided into two generic categories; granulated/powdered and extruded (pre-hydrated). One of each of the generic types were selected for this study to provide a representative overview of the GCL product range. The main type of laboratory assessment was that of fluid migration through the liners. Due to the paucity of knowledge in relation to diffusion, emphasis was put on diffusion assessment. At an early stage in this research, it was found that suitable equipment for the assessment of diffusion was not available and, as a result the author developed two main types of diffusion test cells which were key to this work. These cells were the constant stress and constant volume diffusion cells. In the author's opinion, the constant stress cell, in particular, offers many advantages over current diffusion equipment. During the production of these cells, emphasis was placed on the following factors; sample size, control of effective stress, mixing of fluid, reduction in sample and fluid contamination, reservoir size, sample boundary, reduction of leaks and ease of sampling. Following the development of the diffusion cells, extensive testing was carried out. Using solutions of sodium, potassium and calcium chloride the assessment of contaminants was selectively limited. A concentration gradient was created across the GCL sample by placing a cation solution on one side and deionised water on the other. Following hydration of the GCL samples with deionised water, 1000ppm of prepared solution was placed in the source reservoir whilst fresh deionised water was placed in the receptor reservoir. Samples were taken at regular intervals, from both source and receptor reservoirs, and their concentrations assessed. Profiles of source and receptor concentrations were plotted versus time. A tabulated Microsoft Excel spread sheet was used in the determination of diffusion coefficient. This was achieved by incorporating equations from the concentration plots with Ficks' law. Extensive hydraulic conductivity tests carried out by the author on the GCLs were compared with the diffusion tests. Standard triaxial, Rowe & large column hydraulic conductivity tests were produced. A large part of the investigation was the assessment of the characteristics of the waterproofing core of the GCLs. A number of techniques were adopted for this assessment. These included the following; X-ray Diffraction (XRD), X-Ray Fluorescence (XRF) & Scanning Electron Microscope Analysis (SEM). These assessments provided an overview as to the characteristics of the bentonite core. The SEM, in particular, was used to assess the microstructure of the two types of GCL under investigation and was used to determine if there was any variance in the particle frequency, type, shape and orientation. The XRF and XRD equipment were used to make an assessment of the mineralogy of the bentonite core. These procedures were conducted on a number of available bentonite granules and assessed relative to that of the core product of the GCL under investigation. Tests were also conducted on samples used in the diffusion experiments. Sections of the samples were removed from the source, middle and receptor sides of the samples and taken for analysis. The discussion and concluding remarks of this thesis have highlighted a number of key findings. It was noted that there is a marked difference between the granulated and extruded (pre-hydrated) GCLs assessed. It was found that the extruded (pre-hydrated) GCL exhibits an orientated microstructure. The bentonite particles were predominantly orientated flat across the width of the GCL. The granulated bentonite, when hydrated, did not exhibit any preferential orientation of bentonite particles.
40

Meshless methods : theory and application in 3D fracture modelling with level sets

Zhuang, Xiaoying January 2010 (has links)
Accurate analysis of fracture is of vital importance yet methods for effetive 3D calculations are currently unsatisfactory. In this thesis, novel numerical techniques are developed which solve many of these problems. This thesis consists two major parts: firstly an investigation into the theory of meshless methods and secondly an innovative numerical framework for 3D fracture modelling using the element-free Galerkin method and the level set method. The former contributes to some fundamental issues related to accuracy and error control in meshless methods needing to be addressed for fracture modelling developed later namely, the modified weak form for imposition of essential boundary conditions, the use of orthogonal basis functions to obtain shape functions and error control in adaptive analysis. In the latter part, a simple and efficient numerical framework is developed to overcome the difficulties in current 3D fracture modelling. Modelling cracks in 3D remains a challenging topic in computational solid mechanics since the geometry of the crack surfaces can be difficult to describe unlike the case in 2D where cracks can be represented as combinations of lines or curves. Secondly, crack evolution requires numerical methods that can accommodate the moving geometry and a geometry description that maintains accuracy in successive computational steps. To overcome these problems, the level set method, a powerful numerical method for describing and tracking arbitrary motion of interfaces, is used to describe and capture the crack geometry and forms a local curvilinear coordinate system around the crack front. The geometry information is used in the stress analysis taken by the element-Free Galerkin method as well as in the computation of fracture parameters needed for crack propagation. Examples are tested and studied throughout the thesis addressing each of the above described issues.

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