Underwater Structural Health Monitoring of Composite Navy Propellers

Advanced composite materials are currently being considered for use in propellers on Navy ships. However, limited in-service data exists on the performance of these materials which leads to excessive pre-service testing and a tendency to overdesign components. Therefore, to reduce the excessive testing, overdesign tendencies and implementation time while not compromising safety, there is currently a need for a permanently installed SHM system capable of detecting and characterizing early stages of in-service damage to composite propellers. FBS, Inc. proposes the development of an ultrasonic guided wave approach. The system consists of an array of flexible guided wave sensors which can be surface mounted or embedded inside the composite component. The guided wave sensors can function either as ultrasonic transmitters or receivers in order to send and receive guided wave energy between them. Changes occurring to the received signals due to the introduction of damage can be monitored over time, in real time or periodically, to alert personnel if and when damage occurs. A key advantage of the proposed approach is the fact that guided waves can travel long distances in the structure making it possible to monitor the entire component with only a few sensors mounted at fixed locations.