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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.
21

Static, dynamic and fatigue characteristics of helical cables

Davies, Timothy J. January 2000 (has links)
Extensive parametric studies have been carried out, using the orthotropic sheet theoretical model of Hobbs and Raoof, on a wide range of spiral strand constructions, with outside diameters, d, and lay angles, a, in the practical ranges, 16.4 mm ≤ d ≤ 184 mm, and 11 ≤ α ≤24 , respectively. The effects of an external hydrostatic pressure on certain structural characteristics of sealed spiral strands, used in deep water applications, have also been studied in some detail, for water depths ranging from 0 m to 2000 m. The results, based on such theoretical parametric studies, have, for example, been used to refute claims by Jolicoeur that, by a simple modification, a significant improvement to the original orthotropic sheet model of Hobbs and Raoof , had been found. In addition, using such studies, axial fatigue life design S-N curves have been developed, which cater for the effects of an externally applied hydrostatic pressure on sheathed spiral strands. Simple (hand-based) formulations have also been developed for estimating the maximum frictional axial and torsional hysteresis along with ,the associated axial load range/mean axial load, and range of twist/2, respectively, at which they occur, relating to both, the in-air conditions and also when a sheathed spiral strand is subjected to an external hydrostatic pressure. The previously reported work of Raoof and his associates, in connection with the response of helical cables (spiral strands and/or wire ropes) to impact loading, has been extended to include the development of closed-form solutions for predicting the extensional-torsional wave speeds and displacements, in axially preloaded helical cables, experiencing a half-sine type of impact loading at one end, with the other end fixed. The influence of the lay angle on the response of a spiral strand to three different (i.e. unit-step, triangular and half-sine) forms of impact loading functions, has also been analysed, with much emphasis placed on the practical implications of the final results in connection with non-destructive methods of wire fracture detection under service conditions.
22

Development of mechanical reliability testing techniques with application to thin films and piezo MEMS components

Gkotsis, Petros January 2010 (has links)
This work focuses on the development of a method for probing the mechani- cal response of thin film materials based on miniature tensile testing. A number of mechanisms that may compromise the performance and potentially limit the operational lifetime of MEMS devices which incorporate functional ferroelectric ceramics were also identified and investigated. Reliability of piezo MEMS com- ponents was studied at a wafer and at a device level through the development of appropriate techniques based on miniature tensile testing, time- resolved mi- cro RAMAN spectroscopy and laser Doppler vibrometry. Micro tensile testing was further used for the extraction of the elastic properties of various thin film materials. A miniature tensile stage was developed in common with DEBEN UK for the mechanical characterization of functional thin film materials like PZT and ZnO ceramics, which are commonly used in MEMS fabrication. The stage is of- fered with a piezo electric motor which can be fitted with interchangeable heads. These can be combined with di.erent types of mounting jaws, enabling both con- ventional tensile testing and compression testing to be performed. Strains and displacements were measured in- situ using an optical, non destructive method based on CCD imaging. The elastic constants of polymer (LCP), LCP-Au bi- layers and electroplated Ni were defined in good agreement with the literature. However yield of successfully released ceramic samples was rather poor so a col- laboration with IMTEK at Germany was established. Using their facilities batch processing of a large number of wafers was possible. Cont/d.
23

Arc welding of high strength aluminium alloys for armour systems applications

Pickin, Craig Graeme January 2011 (has links)
The ternary Al-Cu-Mg system 2xxx series aluminium alloys were examined as construction materials for armour system applications based upon comparable ballistic properties to the currently employed Al-7xxx series alloys. Utilising MIG welding solidification cracking was evident when welding constrained Al-2024 candidate base material using Al-2319 filler, the only available consumable wire for this series. A previously developed thermodynamic model suggested that an incompatible weld chemistry resulted when welding with this filler which would result in hot cracking due to a wide weld pool freezing range and a low volume fraction of eutectic liquid. As this filler wire was the only commercially available Al-2xxx filler this was seen as the principal limiting factor for exploiting this alloy series. The solution was to vary and control weld chemistry. Two approaches were taken. Firstly advanced arc welding was used to control weld dilution with the base material. A clad layer exhibiting a less crack susceptible composition was deposited using the Cold Metal Transfer process and the binary Al-2319 filler wire. Onto this layer the same filler could then be deposited to provide a structural joint. Although not fully validated, by limiting weld dilution with the base material this technique showed potential as an alternative method for suppressing solidification cracking. The second approach, which forms the core of this work, adapted the conventional tandem MIG welding process to mix different series consumable fillers in a single weld pool to control weld composition. A range of ternary weld mixtures were produced which resulted in the development of a robust thermodynamic model. Validation using this system resulted in weld cracking being eradicated. The concept was then further developed to weld using three filler wires; this expanded the mixing range and allowed further model validation. A range of crack free compositions were produced with differing mechanical properties. An optimum weld composition was determined that was then used for characterisation of the weldment. By varying heat input, base material HAZ softening was controlled with joint failure confined to the weld / base material interface. This was attributed to grain boundary liquation due to the welding temperatures involved resulting in solute rich grain boundaries. These areas did not deform easily under tensile loading initiating fracture of the joint. Acceptable joint strengths were realised however ductility was reduced due to the identified failure mode. Although not tested to military specifications, acceptable mechanical test values were recorded which were closely compliant with the minimum requirements for armour system specifications. As a consequence a filler wire composition was recommended for future prototype development.
24

An integrated structural health monitoring approach to composite-based pipeline repair

Abd Murad, Mahadi January 2011 (has links)
One of the most common problems in the structural integrity of industrial pipelines is external corrosion. Composite materials have been accepted as a repair option to restore the original strength of the effected damaged section but the approach to analyse how well the composite repair has influenced the stress and strain distributions between the reinforced steel and the reinforcing composite is yet to be determined. This approach is required since it can increase the confidence level among pipeline operators or manufacturers in terms of the composite repair solution that they have chosen or offered. The aim of this study was to develop an integrated approach that could provide a complete methodology to assess the integrity of pipeline systems, especially in quantifying the level of reinforcement provided by the repair in the elastic working region. This cannot be achieved by the traditional method that only relies on classical mechanics derived from strength of materials and compatibility relations. To fulfil this aim, efforts included the simulation of a fibre glass composite repair system using finite element analysis (ABAQUS) software, design and fabrication of the pressure and temperature test rig, installation of fibre glass composite material, and data acquisition. The arc-shaped notch defect that has never been studied before was chosen in the study of stress concentration and bonding integrity of the composite repair system and further validated experimentally using the test rig. The numerical results of this work demonstrated different stress concentration values as the arc-shaped defect size increased. With a proper test plan, the optimum repair system that contains variable lengths of the arc-shaped defect and different lengths as well as thicknesses of the composite material was achieved in the stress distribution study. The bonding integrity via strain distribution study was further validated experimentally. The experimental pressure test results showed some good agreement, especially in the hoop load transfer and limitations of the simulation works were adequately addressed. The experimental temperature results managed to show how the thermal strain behaved in the anisotropic Triaxial Woven Fibre composite repair system. This approach is useful for a better acquisition of information that enables the diagnosis and prognosis of the pipeline repair system prior to installation on site. The novelty of this technique is in its ability to analyse the load transfer in a composite repair system in a more efficient way which can save time and cost.
25

Condition monitoring of gearboxes using acoustic emission

Eftekharnejad, Babak January 2010 (has links)
Acoustic emission (AE) is one of many technologies for health monitoring and diagnosis of rotating machines such as gearboxes. Although significant research has been undertaken in understanding the potential of AE in monitoring gearboxes this has been solely applied to spur gears and slow speed roller bearings. This research presents an experimental investigation that assesses the effectiveness of both AE and vibration technologies in identifying various types of defects on in a helical gearbox; the first known attempt. Furthermore, the application of advanced signals processing techniques such as Spectral kurtosis (SK) and wavelet analysis were studied on AE and vibration signatures. It is shown that the application of advanced signal processing methods is particularly necessary for monitoring helical gears. The application of SK and wavelet analysis was found to be effective in denoising the acquired signals. The first chapter of this thesis is an introduction to this research and briefly explains motivation and theoretical background supporting this research. The second chapter summaries the relevant literature to establish the current level of the knowledge in this field. The third chapter describes methodologies and experimental arrangement utilized for this investigation. Chapter 4 discusses helical gear diagnosis for both natural and seeded surface defect. Chapter 5 reports on an experimental investigation in which several technologies such as AE, vibration and motor current signature analysis, were applied to identify the presence of a naturally fatigued pinion shaft in an operating gearbox. Chapter 6 details an investigation which compared the applicability of AE and vibration technologies in monitoring a naturally degraded roller bearing. It has been concluded that AE is a strong diagnostic tool for early diagnosis of bearings faults. However, the application of condition monitoring for helical gear diagnosis was fraught with some degree of complexity as compared to spur gears. This implies that condition monitoring of the gears using AET can be challenging. On the contrary, the applicability of AET for bearing diagnosis was promising and it offered an absolute advantage over the conventional vibrationdiagnosis. Furthermore, the application advanced signals processing methods such as Spectral Kurtosis and wavelet was found to be promising in denoise the recorded AE signals. It was also concluded that the use of different signal processing methods is often necessary to achieve meaningful diagnostic information from the signals.
26

Modelling and predicting fatigue crack growth behaviour in weld induced residual stress fields

Servetti, Guido January 2011 (has links)
In the last few decades, new design concepts and manufacture processes have been developed in order to reduce the maintenance and manufacturing costs, and structural weight of aircraft components. The integral metallic structure with welding processes is one of the most promising solutions. The exclusion of fasteners and overlapping joints in the airframe reduces the costs, the weight, and eliminates stress concentrations near the holes. The research and development of welding processes for large civil aircraft is in the early stages, thus assessment of their impact on damage tolerance (DT) design must be carried out before the technology can be applied for large civil aircraft. Cont/d.
27

A finite element procedure for assessing continuous flaws in clad pressure vessels

Balasubramaniam, Krishna January 1985 (has links)
No description available.
28

A high-sensitivity resonant sensor realised through the exploitation of nonlinear dynamic behaviour

Waugh, William Haley January 2011 (has links)
Measurements of viscosity and density allow for the monitoring of fluid quality and processes involving a fluid environment. There are various fields in which such measurements may be required, including oil exploration and production, environmental monitoring, process control, medicine, and the automotive industry. Existing MEMS viscometers and density meters typically measure vibrational characteristics such as resonant frequency, bandwidth and quality factor. This thesis reports on the development of a high-sensitivity resonant sensor. In order to significantly improve sensitivity to changes in viscosity and/or density the proposed sensor will exploit nonlinear dynamic behaviour and measure the frequency separation between singular jump points in the frequency response function. By using a one-mode approximation when excited near resonance, the dynamics of a clamped-clamped slender beam immersed in fluid is that of a standard Duffing oscillator. With harmonic forcing of sufficient magnitude, a bistable region, bounded by amplitude jump points, is seen to occur. The width of this bistable region, δF , is dependent on the damping ratio of the system, which is shown to be a function of the dynamic viscosity and density. Experiments with clamped-clamped silicon <100> beams in a range of Newtonian gases demonstrate that the measurand δF can uniquely identify a fluid, and may be amplified to magnitudes greatly exceeding bandwidth measurements for the same device. In addition, the sensitivity of the proposed nonlinear sensor to changes in fluid properties at low viscosity can be at least an order of magnitude better than that of conventional devices. Forcing magnitude and control is identified as being critical to the measured width of the bistable region. Beam dimensions can be chosen to optimise measurements for the desired application.
29

Failure detection of composite joints using data mining

Kia, Shima Shirazi January 2008 (has links)
In structural applications such as in aircraft and spacecraft, composite components are often fastened to other structural members (composite or metals) by bolted joints. In bolted composite structures, stress concentration is developed around the holes and severely reduces the strength of the structure. Uncertainties regarding the strength and failure of critical joints in composite lami!1ates may, on the one hand, lead to conservatively designed joints resulting in significant weight penalties, while, on the other hand, lead to non-conservatively designed joints resulting in catastrophic inservice failure ofthe structure. It is therefore important that the strength and failure of joints in composite laminates be fully understood and that appropriate methods for stress and failure analysis be developed. Current approaches for solving this problem are analytical and numerical methods which are evaluated by experimental tests. In these approaches, the structure is simulated regarding the parameters influencing its behaviour. However, due to the enormous range of influencing factors, no robust formulation has been obtained for this problem. ' In the absence of any comprehensive formulation in predicting the failure of composite pin joints, in this study, a novel application of Computational Intelligence (CI) methods is introduced. One of the main advantages of this approach is its capability of indirectly counting for all influencing factors. The objective of this research is to develop a model (or formula) for predicting the behaviour of pin joints. More precisely, the main question this study answers is: 'Can the behaviour of a pin joint can be modelled, using CI methods, so that its behaviour could be predicted when the design parameters change?' The novel application of CI in predicting the behaviour of pin joints has been implemented on two types of materials, aluminium joints and composite joints, in order to prove its robustness (generality). The problem is categorized as a classification problem and two different methods of classification, decision tree and adaptive neuro-fuzzy system, are applied. In order to improve the accuracy, the hybridization of these two methods is also considered. The analysis presented in this work shows that these techniques can help to solve such an engineering problem through data generated from a limited number of experimental/ analytical tests. The key contributions ofthis research are: 1. Introduction and a thorough examination of the applicability of computational intelligence methods in predicting the behaviour of lightweight (composite and aluminium) pin joints are performed. 2. A set of key parameters is established that define the design space for a generalised lightweight pin joint (and it could be expanded for other structures, as well). Furthermore, based on CI methods, the relationship between the key parameters ofdesign space is developed. 3. The behaviour of lightweight pin joints with variable edge distances are predicted by means of three different types of predictive models. The results are assessed against experimental data. 4. To generalise the application of CI methods, pin joints with variable widths are also modelled using three predictive models. The results are validated against FEA data. 5. The study confirms that based on CI methods, the elastic behaviour of pin joints can be predicted efficiently, using appropriate methods. Specifically, it indicates that the performance of decision tree models in evaluating the potential behaviour of composite joints is superior compared to other methods. However, for aluminium joints, an adaptive neuro-fuzzy system proves to be more efficientand accurate. This is due to the fact that aluminium yields while for composites the material either resists or fails. Therefore, it can be concluded that the material's behaviours should be considered when selecting the data mining modelling techniques. Generally, the performance of adaptive neuron-fuzzy models initiated by C4.5 decision tree algorithms is the most reliable technique for both types ofjoints. 6. Based on CI methods, the possibility of modelling the combinatorial effects of two (or more) different design parameters and their influence on failure of the structure is also confirmed.
30

Stress concentration factors for multiplanar tubular joints

Jandali, M. W. January 1997 (has links)
No description available.

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