Attempts have been made to synthesise a novel siloxane-containing dicyanate ester, 1,3-bis(4-cyanatophenyl)-1,1,3,3-tetramethyldisiloxane, commencing from 4-bromophenol or 4-methoxyphenol. Most of these syntheses have involved the use of a Grignard reaction to form a disiloxane group, followed up subsequent cleavage of an alkyl-protecting group to yield a free phenol. Several different ethers have been attempted, but none was successful. The extreme susceptibility of the aryl silicon-carbon bond to cleavage under acidic conditions has been demonstrated by these reactions. A novel phosphazene-containing dicyanate ester, 1,3-bis(4-cyanatophenyl)-1,3,5,5-tetraphenoxycyclotriphosphazene has been successfully synthesised in a four-step procedure with an overall yield of ca. 35%. The cyanate ester has been characterised by differential scanning calorimetry (DSC), thermogravimetric (TG) analysis, thermomechanical analysis (TMA), 1H, 13C and 13P NMR spectroscopy, and Fourier-Transform Infra-red (FT-IR) and Raman spectroscopy. The thermal data collected showed a surprisingly low glass transition temperature (59 °C) and enthalpy of polymerisation (ca. 36-5 kJ mol-1 of cyanate). The former figure was confirmed by TMA and modulated DSC. However, the cured cyanate showed reasonably high thermal stability: no mass loss was observed before 300 °C. Total decomposition did not occur until about 650 °C.

To evaluate the state of health of the composite, a real-time, in-situ acoustic emission (AE) damage detection system has been developed, where the monitoring of AE activity emitted from within a carbon/epoxy composite material (CFRP) is achieved using an all-fibre Mach-Zehnder interferometric sensor. The basic Mach-Zehnder configuration was modified to achieve the sensitivity needed to detect the low amplitude signals associated with AE. An active homo dyne feedback loop was employed to maintain quadrature, whereas polarisation controllers ensured that the state of polarisation of the guided beams were equal. Two additional components were included in the AE detection system; fibre collimators and a demountable composite test section. The fibre collimators adjusted the optical path length in one of the arms of the interferometer to help maintain system sensitivity from test to test. The demountable test section ensured ease of testing, without the need for continual fusion splicing. The characterisation of the fibre optic sensor was achieved by an analysis of its response to known acoustic disturbances. The fibre optic sensors response to continuous and transient acoustic excitation sources demonstrated the feasibility of using an embedded fibre optic Mach-Zehnder interferometric sensor for the evaluation of composite materials. The sensor's potential for non-destructive evaluation (NDE) was investigated by placing CFRP specimens with the embedded sensors under sufficient tension to cause damage. Signal analysis was performed on the detected AE data, using the time domain parameters and the cumulative event count. The change in the slope of the cumulative count curve coincided with the point where the accumulated damage seriously compromised the structural integrity of the sample. As a damage detection system the fibre optic sensor was adequate, however, the correlation of the time domain parameters with specific damage mechanisms proved inconclusive. Specially designed samples were manufactured to help the fibre optic sensor differentiate between mechanisms. Fibre optic sensor component failure resulted in the testing and analysis using the piezoelectric transducer only. Amplitude and frequency distribution analysis of the piezoelectrically detected signals from these specially designed composite samples was attempted. From the results, it was evident that a correlation could be made between some of the damage mechanisms and the detected AE signals. However, it was apparent that a mixing of distribution occurred in some of the tests. Despite this, the results obtained using the piezoelectric transducer highlighted the benefits of attempting these specially designed tests in future fibre optic sensor work.

The subject of this dissertation is a theoretical and experimental study of electromagnetic and acoustic emission generated in the course of crack formation in solid dielectric materials. Theoretical part of this work is focused on the electromagnetic emission method, because it is related to a number of unsolved problems in the field of generated emission signals measurement, as well as in the field of the correct interpretation of obtained experimental data. Consequently, issues of emission signals detection by capacitance sensors and the transformation of crack primary parameters on the measured variables within the proposed transfer system have been dealt with. The results in this area were an extension of application range of the electromagnetic emission method on composite materials (especially on fiber reinforced polymer composites), identification and evaluation of the most significant emission sources in investigated composites and developing a methodology for evaluating of the crack primary parameters based on the measured emission signals waveforms in time and frequency domain. The experimental part of this dissertation was focused on a complex methodology for emission signals (including data from additional sensors) continual recording, processing and evaluation and for monitoring the response of stressed material to an applied mechanical load in real-time. Partial results from different research areas were also implemented into this methodology. This included the detection of emission signals, design and implementation of the appropriate measuring apparatus, analysis of measured signals in the time and frequency domain and advanced methods for processing and evaluation of measured data.