A full-optical strain FBG sensor for in-situ monitoring of fatigue stages via tunable DFB laser demodulation

Continuously alternating loads and environmental temperature fluctuations can easily cause material aging and fatigue defects in some in-service infrastructures. In order to improve the load-bearing capacities of these infrastructures and prevent unexpected accidents, a flexible continuous detection system that can evaluate the health of these structural systems is needed. The detection system should have the advantages of integrated miniaturization, low cost, high stability and sensitivity, suitability for engineering applications, etc. A full-optical strain sensor based on tunable laser demodulation is designed in this paper. It uses a home-made control mainboard to monitor a 2425-T3 aluminum alloy during tensile and fatigue tests. The tensile test results indicate that the FBG sensor response correlates well with the strain measured using a strain gauge. Therefore, the load and strain can be both monitored via the FBG sensor response. The fatigue test results demonstrate that the FBG sensor presented is superior to the strain gauge and has better sensitivity and stability for vibration monitoring in complex environments. In this letter, we make full use of the FBG’s advantages including its small size and light weight to implement an integrated, miniaturized FBG sensor design with significant structural health monitoring applications.