Effects of long-term exposure on composite manufactured marine propellor blades in pure distilled water and artificial seawater

Authors

Jacob Brady

Document Type

Engineering, Computing and Mathematics Article

Abstract

The aim of this research was to establish the feasibility and investigate the mechanical challenges of the use of composite materials for a marine propellor. Focusing on the major challenge of hygroscopic swelling and the effect this has on material dimensions and properties. Flax-epoxy and carbon-epoxy samples were manufactured and tested in distilled water and artificial seawater to establish the effects of hygroscopic ageing over long-term exposure. Accelerated ageing at 60°C was used to minimise experimental duration whilst observing long-term effects. The research also identified proposed values for the co-efficient of hygroscopic expansion in three planes of 2x2 twill weave epoxy laminates from the described fibres. The issue of increased water absorption in natural fibres with high cellulose content is identified and the subsequent mechanical performance issues as a result of fibre-matrix debonding are explored. Notably, salinity present in artificial seawater had no significant effect on flexural modulus, flexural strength, and inter-laminar shear strength. However, salinity had a significant effect increasing the rate of dimensional changes. These changes were most noticeable in flax fibres where length changes in distilled water were only approximately 20% of those in ASW. However, this research extended beyond its initial scope to identify that immersion time had a significant effect on moisture uptake. Cyclic immersion resulted in degradation of the fibre-matrix interface at a faster rate, with flax samples reaching near saturation 178% faster on the second cycle. Overall, an increase in immersion period results in an increase in moisture content resulting in a subsequent decrease in mechanical properties to varying extents and an increase in dimensional changes. These all are fundamental challenges that must be resolved for the successful application of composite marine propellors. The paper puts forwards recommendations for further study particularly with regards to dimensional changes.

Publication Date

2025-07-30

Volume

18

Issue

1

ISSN

1754-2383

Deposit Date

2025-07-29

Creative Commons License

This work is licensed under a Creative Commons Attribution 4.0 International License.

Recommended Citation

Brady, Jacob (2025) "Effects of long-term exposure on composite manufactured marine propellor blades in pure distilled water and artificial seawater," The Plymouth Student Scientist: Vol. 18: Iss. 1, Article 2.
DOI: https://doi.org/10.70156/1754-2383.1512
Available at: https://pearl.plymouth.ac.uk/tpss/vol18/iss1/2