An optical-fibre fatigue crack-detection and monitoring system

An assessment has been made of the reliability of an optical-fibre crack-monitoring system for detecting the initiation and growth of fatigue cracks in aluminium alloys. The sensors are capable of detecting crack-width increases in the range 5-30 mu m in aluminium alloys subjected to cyclic loading with a high degree of confidence. The performance of the sensors is unchanged by large cyclic loading cycles up to about 100 microstrain, over the temperature range -196-+120 degrees C, up to 100% relative humidity conditions or immersed in normal or sea water. Parallel work showed that the same sensors can be used for detecting cracks in steel, concrete and composites. In the case of composites and also concrete, the sensors can be embedded within the structures during manufacture or construction.