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Techniques for the generation of quantitative ultrasonic images in non-destructive testing have generally involved a substantial cost in terms of data storage and computational time, and have thus found limited application. Preference has therefore been given to the more straightforward imaging methods, such as main beam projection, which detect the presence of defects and provide a limited flaw sizing capability. The relatively small number of flaws requiring detailed examination, coupled with substantial increases in available data storage and computational power, have made it possible to use a number of straightforward tomographic reconstruction methods to produce high resolution images of flaws contained within the material under examination. A set of these images are then fused together using a novel fuzzy logic image fusion technique into a single image from which more accurate measurements of flaw size, shape and orientation can be made. However, if the quality of the raw A-scan data is not sufficiently high then the data will be filtered using Maximum Likelihood Deconvolution (MLD). The aim of this blind deconvolution method is to improve the time resolution and Signal to Noise Ratio of the A-scan data with only knowledge obtained from the data, this is in contrast to the majority of techniques currently used for this purpose. The three tomographic methods which have been implemented in this work are Reflection tomography, Time-of-flight Diffraction tomography and Transmission tomography. In addition a Single Bounce Image Enhancement method has been developed to improve the images. Selection of images used in the fusion process depends on the nature of the flaw, as each of these methods identifies different characteristics of the flaw shape. The components of the imaging system have been validated experimentally by the generation of high resolution images from a variety of flaws contained within cylindrical aluminium test specimens.

The purpose of this thesis is to assess and develop a non-destructive evaluation (NDE) procedure for evaluating the integrity of rectangular and square reinforced concrete (RC) slabs. This procedure employs both dynamic frequency and deformation response signatures to track changes in the slab following dynamic excitation. Such a procedure could provide a good basis for practising engineers to conduct nondestructive testing (NDT) and evaluation of general RC structures. The response of RC floor slabs to dynamic excitation have been experimentally studied at 1/3rd scale for two aspect ratios (square and rectangular), three concrete grades, and with and without cement replacement under clamped edge conditions. The model slabs were subjected to series of quasi-static loading and unloading sequences, to increasing load levels until failure was reached. At the unloaded part of each load cycle, the slabs were subjected to dynamic excitations, alternately using a hand-held, Bruel and Kjaer (B and K) impact hammer, and broad-band burst chirp shaker excitation. For the larger square slabs, at each unloaded part of the load cycle, a 265 gm steel ball bearing dropped from a fixed, standard height to provide more robust impulse excitation. All of the slabs were instrumented with optimally located accelerometers and strain gauges to capture the slab responses. The acceleration, deflection and strain readings resulting from the dynamic excitation were recorded at incremental load steps, from the initial unloaded state up to failure, and subsequently evaluated and analysed. The results show that the changes resulting from damage are readily observable, in the fundamental and higher modes of vibration and in the load-deflection and strain responses. These changes have been examined and analysed in both the time and frequency domains, and using other techniques, to establish the viability of this approach in evaluating the integrity of RC and other complex structures.

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Thesis (M. Phil.)--University of Hong Kong, 1993.

Rayleigh scattering, that is the elastic and coherent scattering of photons from bound atomic electrons, has been investigated for use as an active probe for substance identification. An angular dispersive scattering system has been developed for materials identification utilising the 22 keV Kalpha X-ray line from a low power (25 Watt) silver anode X-ray tube. Differential scattering cross-sections have been measured for a wide range of low- to high-Z materials and compared with free atom theoretical predictions. Experimental results compare favourably with theory and evidence has been found to suggest that inter-atomic and inter-molecular interference effects have little or no effect upon the total scattering cross-section. The potential of Rayleigh scattering for detection of inclusions of low-Z media within extended objects of similar atomic constitution has been investigated with particular emphasis on the detection of potential contaminants in food products. The contrasts obtained with scatter techniques are substantially in excess of those achievable with conventional transmission measurements. By exploiting the ratio of the scattering in two regions of momentum space as the scatter parameter the contrast between inclusion and matrix may be increased to over five times that of transmission methods. This technique may be used in many situations where alternative photon interrogation methods such as X-ray transmission or X-ray fluorescence are unsuitable and a wide range of potential applications including quality control, sorting of plastics, security screening and oil/water discrimination have been considered.