Structural Health Monitoring of Composite Marine Propellers using Embedded Piezoelectric Sensors

Abstract

Society increasingly demands that ships become more sustainable and quieter, given their significant share of global fuel consumption and green-house gas emissions. Fiber-reinforced composite marine propellers can contribute meaningfully to these goals. As a promising alternative to the conventional rigid metallic propellers, flexible composite propellers can offer improved underwater radiated noise (URN) and propulsion efficiency. Furthermore, manufacturing propellers from fibre-reinforced composite materials makes them lighter and reduces their electromagnetic signature.

Despite the significant potential of composite propellers for marine propulsion systems, uncertainties in their fatigue behaviour have so far hindered their wide-spread adoption. These uncertainties can arise from imperfections during the manufacturing process, operational conditions different than the ones considered in the design, coating deterioration leading to water ingress, impact events, and more. Such factors can have significant impact on the lifetime of the propeller, which is typically expected to endure billions of cycles. Structural health monitoring (SHM) has the potential to mitigate this issue by real-time recording and assessing the structural response and integrity of the propeller. Such an SHM system should neither affect the propeller performance nor its load-bearing capacity. In addition to providing insights into the current structural integrity of the propeller, an SHM system may also enable enhanced estimation of the remaining lifetime, thereby minimizing the risk of unexpected failures and downtime.

This thesis investigates the feasibility of developing composite marine propellers with an embedded SHM system based on piezoelectric sensors. These sensors are capable of performing strain monitoring (with application in load/response estimation) and acoustic emission monitoring (with application in damage identification). Three main topics have been studied; (i) the feasibility of measuring dynamic strains in the propeller blade using the embedded sensors, (ii) the effect of embedding piezoelectric sensors on the structural integrity, and (iii) the feasibility of measuring and assessing damage-induced acoustic emissions using the embedded sensors. An analysis framework has been proposed for the identification, classification, and localisation of acoustic emissions in thick composite structures…