The optimisation of the interdigitated electrode (IDE) design for active fibre composites was performed using finite element analysis. The effect of the IDE geometry (electrode width and spacing) and electroceramic substrate thickness on the developed strain for bulk PZT substrates was modelled. The modelling results show that the highest strain is generated when the electrode width equals half the substrate thickness and for thin substrates the electrode finger spacing can be reduced to enable lower driving voltages. Approximately 80% of the maximum d 33 strain can be achieved with an electrode separation to substrate thickness ratio greater than 4. The results present simple coherent guidelines for the optimisation of electrode geometry for piezoelectric actuators and active fibre composites.

Piezoelectric materials are capable of actuation and sensing and have found uses in applications including ultrasonic transducers, hydrophones, micropositioning devices, accelerometers, and structural actuators. A composite con-® guration for structural actuation having signi® cant advantages over conventional piezoelectric actuators has been conceived, and the recent development of piezoelectric ceramic ® bres 5100 l m in diameter has enabled this concept to be realised. It is envisaged that these composites will ® nd uses in contour control, non-destructive testing, vibration suppression, and noise control. The possibility of computer control using closed loop systems has led to these composites emerging as potential `smart' materials and structures. Since their conception, less than a decade ago, signi® cant advances have been made in many areas concerned with composite performance, such as ® bre and matrix technology and con® guration optimisation. These advances are charted, the ® bre, matrix, and electrode technologies are reviewed, and the manufacture, modelling, and applications of these new piezoelectric composites, known as active ® bre composites, are discussed.MST/5547

With the rapidly escalating usage of composite materials, not only in military aircraft but in civil airliners as well, production NDT throughput is already stretched to its limit internationally. NDT data analysis is set to become the bottleneck preventing the required rise in production rates of composite civil aircraft in the next few years. Thus there is an urgent requirement for rapid, automated analysis of up to a Terabyte of data per airliner, escalating to over 200 Terabytes per year-worldwide. The primary aim of automated analysis is to release operators from the time-consuming analysis of all scans and focus operator attention on non-compliant structures. A secondary aim is to provide threedimensional quantitative information that lightens the operator's decision-making burden. Through advanced characterisation methods, NDT also has the potential to provide crucial feedback to control the composite production process, increase production yield and decrease costs. Current analysis methods for ultrasonic scans produce through-thickness average parameters, which provide little useful information to assist the stress analysis for defects, or the production process. Three-dimensional characterisation of defects can increase yield by informing the concession/disposition process for defects. For future process control, information is required about the 3D distribution of material properties in the structures on the production line, providing comprehensive long-term trend analysis. 'ANDSCAN' is a Registered Trademark of QinetiQ Ltd. 'StackScan', 'Ply Fingerprinting' and 'PinPoint' are Trademarks of QinetiQ Ltd. 'MLM-PropMat' is a Trademark of the University of Nottingham. Patents have been filed by QinetiQ Ltd covering the technology described in this paper.

No abstract

Ultrasound has been used to inspect composite laminates since their invention but only recently has the response from the internal plies themselves been considered of interest. This paper uses modeling techniques to make sense of the fluctuating and interfering reflections from the resin layers between plies, providing clues to the underlying inhomogeneities in the structure. It shows how the analytic signal, analyzed in terms of instantaneous amplitude, phase, and frequency, allows 3-D characterization of the microstructure. It is found that, under certain conditions, the phase becomes locked to the interfaces between plies and that the first and last plies have characteristically different instantaneous frequencies. This allows the thin resin layers between plies to be tracked through various features and anomalies found in real composite components (ply drops, tape gaps, tape overlaps, and out-of-plane wrinkles), giving crucial information about conformance to design of as-manufactured components. Other types of defects such as delaminations are also considered. Supporting evidence is provided from experimental ultrasonic data acquired from real composite specimens and compared with X-ray computed tomography images and microsections.