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A smart structure is one that senses its internal state and external environment, and based on the information gained responds in a manner that fulfils its functional requirements. The primary advantage of moving towards smart structures technology is the potential cost benefit of condition-based maintenance strategies and the prospective life extension that may be achieved through in situ health monitoring. The monitoring of operational health and performance, and diagnosis of any faults as they occur, is a relatively new concept that is being developed globally to provide advantages of safer , more reliable and affordable structures. Health monitoring can be achieved by positioning (embedded or surface mounted) sensor systems on a structure to measure those physical parameters that are informative with respect to the state of the structural health. Information relating to the severity and location of damage, as well as to the nature of the loading is of obvious importance to this endeavour.In the aerospace industry bonded composite patches are increasingly being used to extend the operational life of ageing aircraft. The application of bonded composite patches to repair or reinforce defective metallic structures is widely acknowledged as an effective and versatile procedure. Such patches have been successfully applied to the repair of cracked structures, to the reinforcement of components subject to material loss due to corrosion damage and as a general means of stress reduction through the provision of a supplementary load path. However, certification requirements mandate the need for a methodology for monitoring the damage state of both the defective underlying structure and of the repair. In this case the concept of smart structures can be used to detect damage in the repair itself as well as monitor damage growth in the parent structure.This paper reports on the development of a 'perceptive repair' or 'smart' system which will provide information on the in-service performance of the repair and the associated structure. In this respect, this paper focuses on the detection of disbond in the adhesive layer between adhered and the metallic parent structure. One of the criteria of this smart system is that it must be economical, reliable and, preferably, self-powered. To this end, it was proposed that piezoceramic of piezoelectric material be utilized because of their ease of application. These materials were chosen because they can be used both as a actuator and as a sensor. This paper presents a set of numerical investigations performed to highlight the viability of using this material system, and the associated signal analysis that can be employed to detect the presence or the development of disbonds in the adhesive in a bonded repair situation.

This article presents the development of a process by which an impact experienced by a track-like structure can be reconstructed based on its vibration response. The process is essentially based on an inverse analysis technique, while a cepstral analysis technique is also used to improve waveform reconstructions. Firstly, a finite element (FE) model of a simple track structure was generated and calibrated to a real laboratory model to show that it was able to simulate impact events. The rail geometry was then replaced with a simple rectangular beam in order to allow simulation of a rolling wheel by means of a moving mean load. The simple beam geometry was necessary because the rail geometry carried an excessive computational cost when incorporating a moving mean load. This is a legitimate substitution because the inverse analysis technique is geometrically independent. It was found that the acceleration response of the track structure due to the dynamic impact was largely unaffected by the moving mean loading condition. It was also found that the inverse analysis technique shows potential for reconstructing input forces, but in some instances the reconstructed waveform has ambiguous peaks and excessive signal pollution around the force waveform. The cepstral analysis was then found to be useful in sufficiently ‘smoothing’ the transfer function spectrum such that an improved waveform reconstruction could be obtained. An error analysis showed that the regular transfer function as obtained by the inverse analysis technique when ‘smoothed’ by cepstral analysis gave a lower order of error. It was found that to provide sufficient coverage of a full crib of rail, three calibration points were required for the transfer function, with four accelerometers to pick up the track responses along the crib.