Multi-functional fibre Bragg grating sensors for fatigue crack detection in metallic structures

Abstract This paper investigates the use of multi-functional fibre Bragg grating (FBG) sensors for structural health and usage monitoring. It is shown how FBG sensors can be used simultaneously for both a strain-sensing-based load-monitoring system and a Lamb-wave-based damage-detection system. Structural health and usage monitoring has gained considerable interest in engineering technologies. Especially for the aircraft industry where damage can lead to catastrophic and expensive failures and the vehicles involved undergo regular cost intensive inspections, a health and usage monitoring system (HUMS) has one of the highest payoffs. Although different approaches for an HUMS can be found in the literature, a system based on the fusion of load monitoring and damage detection could provide highest potential for implementation in future aircrafts. For this paper, initial tests have been carried out to demonstrate the dual load and damage monitoring on a simple aluminium plate. A fatigue test was carried out to study the crack propagation of the plate. FBG sensors were used to record the load history of the test. For the fatigue analysis, the crack growth was observed using a conventional method and the Lamb-wave analysis. Piezoceramic transducers and the same FBG sensors that already monitored the load history were applied to record the Lamb-wave signals. A novel damage index that correlates the sensor signals with the crack length is introduced. Subsequently, the results obtained for both transducers are given and their performance is compared. Final remarks on this initial test of a dual load and damage-monitoring system based on FBG sensors conclude the paper.