BID FOR LIGHTWEIGHT TOPSIDE STRUCTURES
A pan-industry research consortium investigating the use of composite superstructures in shipbuilding plans to start tests with a demonstration product later this year, writes David Tinsley.
The ultimate aim of the EU-sponsored Qualify project is to foster the widespread use of adhesively bonded hybrid (steel/composite) structures, through technical and performance evaluations and the development of certification guidelines.
Led by the Materials Innovation Institute (M2i) in the Netherlands, the 11 partners in the Qualify endeavour comprise shipyards, classification societies, technology providers and academia, with a further 16 companies and organisations participating as observers. Some 60% of the project’s budgeted costs of EUR3.8 million (US$4.2 million) are being covered from the public purse, through a EUR2.3 million (US$2.6 million) allocation by the European Regional Development Fund as co-financier of the Interreg 2 Seas programme.
The case for composites rests on lighter weight and manufacturing advantages relative to traditional steel superstructures. It is suggested that a 10% reduction in the top weight of naval ships, for example, can lead to fuel savings of 1-7%, with a corresponding diminution of emissions.
While steel-to-steel joints can be welded, the construction of vessels comprising a composite superstructure on a steel hull calls for an alternative solution that can offer a strong and safe bond. Although a bolted assembly is practicable, it has cost and performance drawbacks. Another option in forming a secure joint is the use of adhesive as a medium layer between the two construction materials. The three-year Qualify project is addressing the need for greater understanding of the long-term behaviour of hybrid joints and the lack of appropriate guidelines for their approval and design.
Through a rigorous test campaign with adhesive joints, the Qualify partners will gain insights into long-term performance in demanding marine conditions. These insights will inform the development of application guidelines, paving the way to increased use of adhesively bonded structures in shipbuilding. The remit of the project also includes the formulation of a structural health methodology for in-situ monitoring, encompassing early prediction of damage, assessment of damage-detection sensors, and an inspection framework incorporating non-destructive testing(NDT) techniques.
The shipbuilding contributor to the study, the Damen Shipyards Group, is producing joint samples for testing, using a methyl methacrylate(MMA) so as to offer a more flexible, adhesive bond. Several months of experiments will be conducted, in accelerated ageing and dynamic loading conditions, with a view to ensuring performance in service to a predictable level for up to 25 years. Such research is ground-breaking in character. Test work is the province of TU Delft, Gent University, University of Cambridge, and Knowledge Centre WMC.
Adhesive bonding and lightweight materials have been widely adopted in the aerospace and automotive industries, but the take-up in shipbuilding, and especially as regards the construction of large merchant vessels and naval ships, has lagged behind, hampered by the lack of application standards.
As pointed out by the University of Cambridge, “The manufacturing processes in the aerospace and automotive industries are often conducted in controlled environments where dust and debris are uncommon and the temperature is regulated, whereas shipbuilding operations are often exposed to the open air, making the tight process control required for effective adhesive bonding more difficult. This difficulty contributes to general concerns regarding the reliability and fatigue life of an adhesive bond exposed to a harsh marine environment during its service lifetime.”
Due to be completed by the end of July 2020, the project has been organised into distinct work packages, with three principal objectives:
· Evaluation of the long-term mechanical performance of the adhesively bonded joint under representative operational and environmental conditions;
· Development of a reliable inspection and health management methodology for in-situ monitoring of hybrid adhesive joints;
· Development of guidelines for the qualification of adhesively bonded joints in marine and offshore structures.
Qualify is also intended to provide knowledge that can benefit other sectors, such as the substitution of metallic parts by hybrid structures in wind turbines.
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