Highly non-linear sensing devices in structural health monitoring
Description
Sensors in traditional non-destructive testing (NDT) are usually working in a quasi-linear mode. However, this raises a number of difficulties when these sensing principles are applied to structural health monitoring (SHM). Base-line variations and complex sensor data due to diverse interferences with complex structures are one of the main obstacles for a broad-scale implementation of SHM in e.g. aircraft and civil structures. There were diverse solutions proposed to tackle these problems, such as advanced data processing and dedicated high-end hardware components. However, those excessive hardware requirements will in turn involve extra power supply and technologies for robust and extended data storage and processing. All these elements establish serious obstacles for a fast implementation of SHM in routine maintenance operations; not to forget the limited coverage inherent to some of those systems. Besides the idea of focusing and limiting monitoring to selected hot-spots for avoiding large scale monitoring, an interesting alternative is offered by highly non-linear sensing devices. They are characterized by a sharp sensor response depending on an outer parameter that is related to a certain damage threshold. The highly non-linear behaviour is in this way an ideal tool to filter out baseline variations and thus, the probability of detection is superior with respect to many other technologies. In the literature, there are a couple of highly non-linear sensing devices reported and even applied in operational practice, such as the alarm wires in bleed air systems for aircraft providing information on overheat, or crack gauges in fatigue testing. The presentation is intended as a small review on the different sensing principles applied for highly non-linear sensing devices. In general, the underlying physical principles for data reading our are in most cases electrical conductivity or optical transmission. Finally, a number of examples are presented that were already implemented, such as devices for the detection of corrosive liquids in aircraft (Boeing 737-500, Boeing 747-400) and chemical plants.
Files
ECNDT2018-Pfeiffer-et-al.pdf
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(481.7 kB)
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