Experimental study on in-situ internal stress monitoring of full-size water-lubricated journal bearings by embedded fibre Bragg gratings

Real-time stress evolution inner water-lubricated bearings (WLBs) in service time is unaware due to its installation position and harsh surroundings on ship, which will be of vital importance for identifying bearing fault such as abnormal wear or frictional noise. In this work, we present an embeddable sensor based on fibre Bragg gratings (FBGs) and applicate it for bearing internal stress characterization. The developed sensor shows excellent sensing accuracy and repeatability. Integrating FBG sensors into a full-size WLB achieves the in-situ static and dynamic stress monitoring in test rig experiments. Stress distribution along bearing axis was revealed. Dynamic stress inner bottom lining was recorded and analyzed during running-in, pulse excitation, load or rotary speed tests as well as start-up/stop experiments. The outcome indicates that FBG sensors are able to readily detect external impact on shaft and nicely monitor stress variation inner bearing lining. Averaged stress and its variation amplitude reduce with shaft speed rising. It is also interesting to note that the periodically dynamic stress in lining is consistent with shaft speed, which can even reflect shaft speeding up/down. This study provides a novel strategy of utilizing FBG for status monitoring and fault diagnose of WLBs.