The future of composites for marine applications

  • Oliver F Parks

Student thesis: Doctoral ThesisEngineering Doctorate (EngD)

Abstract

Composites are commonly applied in the marine industry due to their high strength-to-weight ratio, improved corrosion resistance, and ability to be moulded into continuous complex geometries. However, some industries have been slow to adopt these new materials due to numerous technical and commercial challenges. This thesis presents a comprehensive investigation into the most critical challenges currently preventing more widespread use of composites in the marine industry.

Typical marine structures are designed to withstand harsh environmental conditions at sea over a 30-year service life. It is crucial to understand the long-term change in material properties due to exposure in this environment. However, it can be difficult to theoretically predict these changes as they are dependent on multiple factors, including the production process, manufacturing variations, environmental conditions, and selected constituent materials. Accelerated conditioning experiments are typically conducted on representative laminates to simulate exposure to harsh conditions over the service life. These tests can be time consuming and costly, so investigations have been conducted by the author to investigate the viability of further accelerating the conditioning process on a range of marine composite laminates. The results indicate that further acceleration leads to, on average, greater knockdowns in laminate strength. The investigation also found a significant variation in seawater degradation amongst a range of marine composite laminates, highlighting the importance of durability testing. The selection of “standardised laminates” is suggested as a means of focusing global research in this area, thus improving long-term durability predictions, and increasing confidence in large marine composite structures. A potential trend between laminate moisture uptake at saturation and strength degradation was also identified which could be used with numerical predictive tools to further simplify initial material down-selection in industry.

A lack of affordable and robust manufacturing processes was identified as a key limitation currently preventing the use of composites in primary structures of large (50m+) commercial vessels. To address this, a rapid manufacturing process development approach is proposed based upon experimental trials and expert industry knowledge. Using this approach, a manufacturing process has been developed for a 75m hull shell and validated via the production of a full-scale demonstrator section. Vacuum assisted resin infusion was selected as the most appropriate production method for this case study as it enables large composite structures of sufficient quality to be manufactured in a relatively affordable manner. Glass fibres and toughened vinyl ester resin were used to manufacture this structure. The greatest challenge of this work was achieving a one-shot 6m vertical infusion with approximately 1 tonne of resin. A full-scale demonstrator was successfully produced; however, the financial risks associated with applying this infusion procedure to a 75m hull cannot be ignored. Whilst the infusion process can tolerate changes in ambient temperature and layup tolerances, the use of a vacuum bag at this scale leaves this process highly susceptible to air leaks. Therefore, whilst the process is technically viable, further improvements should be made to improve commercial viability.

Commercially available automated manufacturing technologies are investigated to reduce process risk and production costs of the selected case studies. Automated production line concepts are proposed, including the automated modular construction of a hull shell assembly using pre-infused panels. This work acts as a first step towards automating the production of large composite hulls and tidal turbine blades, highlighting the key challenges and areas of future development. Further work is required to conduct further structural design iterations, develop a robust panel assembly procedure, and integrate individual automated manufacturing solutions into a complete production line.

The proposed durability prediction and rapid infusion development methodologies, procedures for manufacturing large composite structures, and automated production line concepts presented in this thesis provide the marine industry with tools to support the implementation of composite materials across a wider range of applications in a more cost-effective and lower risk manner.
Date of Award26 Nov 2020
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorPaul W Harper (Supervisor) & Sonya Rusnakova (Supervisor)

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