No description available.

This thesis describes a theoretical and experimental investigation of electromagnetic methods for the detection and measurement of metal fatigue cracks. The available methods are reviewed, with particular attention being paid to mathematical models, and a new model of the electromagnetic field near a metal fatigue crack for small skin-depths is presented which uses a surface impedance boundary condition with the addition of a line source to represent the crack. This leads to a coupled system of two magnetic scalar potentials, one on the crack face which obeys the two-dimensional Laplace equation and one outside the test-piece which obeys the three-dimensional Laplace equation. The behaviour of the field is governed by a parameter m =l/(μ, δ), where l is the size of the field perturbation, μ, is the relative permeability and δ is the skin-depth. When m is small, almost all the flux is concentrated inside the metal and the exterior potential also obeys the two-dimensional Laplace equation, on the test-piece surface. When m is large, the perturbation part of the exterior field has a negligible effect on the field inside the crack so that the crack-face potential may be found by the Born approximation. The general m problem is solved for rectangular and semi-elliptical cracks in flat plates, interrogated by uniform fields, and the solution is verified experimentally. A method for calculating the crack depth from the magnetic field is given, with descriptions of industrial applications. The theory is further developed to find the impedance change in an air-cored circular coil caused by a crack, to find the field near overlapping cracks and to find the field near a crack in an interior corner. Finally, a semi-empirical analysis is presented for a ferrite-cored measuring coil.

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The main aim of this research was to improve laboratory test methods for describing pavement foundation materials so that analytical design based on appropriate mechanical parameters of materials could be performed in practice. The study started by assessing the relevance of currently available methods to describe materials in pavement foundations and reviewing factors influencing the responses of these materials to repeated loading. Two simplified repeated load triaxial apparatuses of different sizes have been developed and their capabilities in characterizing materials in sub-base and sub grade layers have been examined. The large one is for specimens of size 280 mm diameter and 560 mm high and is suitable for full scale Department of Transport Type 1 sub-base granular materials. The small one is for cohesive soil specimens, either recompacted or undisturbed, with a diameter of 103 mm and height of 206 mm. Both apparatuses are equipped with simple loading mechanisms, user-friendly computer data acquisition systems and high precision on-sample, but easy to fix, instrumentation to monitor axial and radial displacements. A complete testing method necessitated the provision of the associated testing techniques. The whole test, including aggregate and soil preparation and testing, was designed to be conducted by one person. Development of the test procedures is detailed. Evaluation of the simplified repeated load apparatuses and the testing techniques involved testing 13 aggregate specimens and more than 26 soil specimens. Furthermore, comprehensive preliminary tests have been performed on the tested materials to provide background information which enabled results from the simplified repeated load triaxial apparatuses to be assessed in detail. For unbound granular materials, the tests included a series of particle examinations and shear box testing. For soils, besides classification tests, the soil suctions and the permanent deformation development under wheel loading were examined. To check the reliability of the two simplified facilities, tests were also carried out on pre-existing sophisticated repeated load triaxial apparatuses. Comparison of aggregate test results has enabled further understanding of the effects on resilient strain, permanent deformation and compressive strength of grading, density, shape, surface profile, surface friction and material type to be gained. Effects from waveform and frequency of load pulses were also discussed. For-soils, sufficient test results not only allowed different materials to be compared but also permitted models to describe resilient strain behaviour and permanent deformation development to be developed.

No description available.

No description available.

The Climatic Wind Tunnel (CWT) is a facility used by the motor industry to test vehicles under climatic extremes without the need for expensive overseas test programs. This work focuses on the application of computer simulation to the Heating Ventilation and Air Conditioning (HVAC) plant that makes up a CWT facility. The objective being to reduce its operational costs through the identification of energy saving operational strategies. When in operation the CWT has a peak power consumption of 3MW. The implementation of any measures that would reduce this peak load would give rise to considerable savings in the operating costs of the facility. Computer simulation is an accepted technique for the study of systems operating under varying load conditions. Simulation allows rapid analysis of different strategies for operating plant and the effectiveness of achieving the desired effect without compromising the buildings performance. Models for the components of the CWT have been developed and coded in Neutral Model Format. These models have then been linked together in a modular simulation environment to give a model of the complete plant. The CWT plant naturally decomposesin to four major subsystems these being the test chamber, the soakroom, air make-up and refrigeration system. Models of all the primary and secondary HVAC plant are described as is how they constitute the systems that make up the CWT. Validation tests for individual components as well as for the systems have been carried out. To illustrate the potential of the application of computer simulation into finding improved modes of operation that would reduce the energy consumption of the facility, four studies have been carried out. The studies involve the possibility of scheduling the operation of condenser fans as a function of refrigeration load and outside ambient temperature, methods for the pre-test conditioning of a vehicle, a reduction in the secondary refrigerant flow temperature and an increase in the thickness of the insulated panels from which the facility is constructed. The studies carried out showed that there was potential for moderate energy savings to be made in the operation of the facility and that extended simulation runs would allow for the in-depth assessment of a large range of possible modes of plant operation in order to identify the areas where the greatest savings are possible.

No description available.

Although small scale magnetic suspension and balance systems (MSBSs) for wind tunnel use have been in existence for many years, they have not found general application in the production testing of flight vehicles. One reason for this is thought to lie in the relatively limited range of attitudes over which a wind tunnel model may be suspended. This text reports on the modifications made to an existing small MSBS at Southampton University to permit the suspension and control of axisymmetric models over an angle of attack range from less than zero degrees to over ninety degrees. Previous work had shown that the existing arrangement of ten electromagnets was unable to generate one of the force components necessary for control at the extreme attitudes. Examination of possible solutions has resulted in a simple alteration which rectifies this deficiency. To generate the feedback signals essential to control the magnetically suspended model, an optical position sensing system using collimated beams of laser light illuminating photodiode arrays has been installed and tested. An analytical basis has been developed for distributing the demands for force and moment needed for model stabilisation amongst the electromagnets and over the full attitude range. This has been implemented by an MSBS control program able to continually adjust the distribution for the instantaneous incidence in accordance with pre-scheduled data. Results presented demonstrate rotations of models from nought to ninety degrees at rates of change up to ninety degrees per second, with pitching rates rising to several hundred degrees per second in response to step-change demands. A study of a design for a large MSBS suggests that such a system could be given the capability to control a model in six degrees of freedom over an unlimited angle of attack range.

Current methods for assessing the integrity of ground anchorages during service are primarily restricted to monitoring by load cells or load lift-off testing. Both are expensive and lift-off testing is time consuming and can damage the anchorage construction below the anchor head. Hence, only typically 5-10% of anchorages are monitored in service. As a result, The Institution of Civil Engineers reported that non-destructive test methods for ground anchorages need to be developed as a high priority (ICE, 1992). The Universities o f Aberdeen and Bradford have been conducting research since 1986 to investigate the response o f rock anchorages to dynamic loading arising from blasting operations. Full scale field trials were conducted during the construction of two tunnels in North Wales. An important finding from the research revealed that certain characteristics of the dynamic response of a rock bolt resulting from blasting operations, were similar for different blast sequences. This indicates that the dynamic response o f an anchorage system is dependant on the construction of the anchorage and the characteristics of the co-vibrating rock mass. Consequently, the University of Aberdeen has developed a new non-destructive condition monitoring and integrity assessment system for ground anchorages (GRANIT ™). A range of patent applications have been successful world-wide and the system has been exclusively licensed to AMEC Civil Engineering Limited. The system operates by applying an axial tensile impact load to the free end of an intact anchorage immediately after installation. The resulting vibrational response is monitored by an accelerometer, located at the anchorage head, which produces a datum signature for that anchorage. The condition of the anchorage is then inferred by comparing subsequent response signatures with the datum. A change in the signature indicates that there may be a potential change in the integrity of the anchorage. Artificial Intelligence systems are employed to compare response signatures. As part of the research programme, the author conducted commissioning tests on small scale laboratory test rigs and was responsible for the development of a prototype non-destructive test system, which included a means of applying an impact load and recording the vibrational response. In addition, the author conducted full scale laboratory tests and field trials to investigate the effect of prestress on the dynamic response of ground anchorage systems. As a result, the prototype non-destructive test system has been employed to successfully predict the amount of load within an anchorage installation.