Marine propellers made of fibre-reinforced composites have demonstrated the potential to outperform metallic propellers in terms of efficiency and under-water noise radiation. For full realisation of this potential in a tailored design process with realistic constraints, accurate information on the hydrodynamic loads acting on composite marine propellers and the structural integrity is of key importance. It is conceptualised that this information can be acquired without disturbing propeller hydrodynamics using a network of piezoelectric sensors embedded inside the blade. In this paper, feasibility of this concept has been investigated numerically and experimentally. Hydrodynamic loads on a composite propeller obtained from numerical simulations were used to assess the sensitivity of piezoelectric sensors in measuring the dynamic strain field due to the blade deformation. Subsequently, 25 small-scale carbon-epoxy composite samples were manufactured with embedded piezoelectric wafer sensors of different sizes, and subjected to non-destructive and destructive loading scenarios. Feasibility of measuring strains at different frequency ranges and damage-induced acoustic emissions was quantitatively assessed from these experiments. Furthermore, the influence of the embedded sensors on the ultimate strength and toughness of the specimens was investigated. It was found that at least 92% of the studied propeller blade would have dynamic strains measurable up to the first four harmonics by the considered piezoelectric sensors. In a four-point bending setup, it was additionally demonstrated that the embedded piezoelectric sensor captured damage-induced acoustic emissions up to specimen failure with an average signal to noise ratio of 17 dB. The results indicate that embedded piezoelectric sensor networks can have the capability to measure both low-frequency dynamic strains in composite marine propeller blades and damage-related acoustic emissions.

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As a primary component of the marine propulsion systems, ship propellers have been traditionally made of nickel-aluminium-bronze (NAB) or manganese bronze (MB). With the development of fibre reinforced composite materials, the advanced plastic materials are considered to be applied in the manufacturing of marine propellers. Compared to conventional rigid propellers, the composite marine propellers are expected to possess advantages of lighter weight, lower maintenance costs, higher cavitation inception speed, declined acoustic signature, and improved efficiency at off-design conditions. These potential benefits have promoted numerical and (fewer) experimental investigations of composite marine propellers. This supports the promising future of their applications, however, a more profound understanding of the underlying mechanical properties of composite marine propellers is essential before they find a wider use in practical applications in engineering.@en