Qualify: Plotting a course for lightweight topside structures
Efficiency and sustainability are big issues facing most industries today, and none more so than marine operations. Damen Shipyards Group’s partnerships with Skoon and EMAR to promote sustainable propulsion are examples of its investment into preparations for a changing future. In a related venture, together with ten other stakeholders, Damen forms the Qualify project partnership to investigate the use of composite materials in the construction of primary maritime structures.
Ship superstructures are traditionally made of steel, thanks to the metal’s malleability in production and durability in operation. Its density, however, makes for heavy vessels – and heavy vessels demand high energy for propulsion. Composite superstructures can be more lightweight, offering greater manoeuvrability and requiring lower combustion volume: a 10% reduction in the top weight of naval ships can lead to a 1%-7% reduction in their rate of fuel consumption.
In the construction of ships comprising a composite superstructure on a steel hull, the two materials need to be joined with a strong and safe bond – but how? While steel-to-steel joints can be welded, steel-to-composite joints require an alternative solution.
One solution for assembly is to bolt the two materials together at the joint. As a shape-bound connection, bolting is relatively straightforward. A major drawback of this method, however, is that it increases the construction cost and lowers the mechanical performance of the vessel. Another option in forming a secure joint is the use of adhesive as a medium layer between the two construction materials. The long-term behaviour of hybrid joints is not yet understood, and the lack of correct guidelines for their approval and design has prevented their uptake by the maritime industry.
This is the focus of the Qualify project.
Please follow the link to discover Qualify project video.
Facilitated by financial support from the EU and Interreg 2 Seas programme, The Qualify project will conduct rigorous testing on adhesive joints in order to provide reliable insights into their long-term performance operating in demanding marine environments. These insights will inform the development of guidelines of their application, which will ultimately enable the increased use of adhesively bonded hybrid structures in primary constructions in shipbuilding.
In addition to testing the joints and informing guidelines for their application, the project aims to produce a structural health management methodology for in-situ monitoring. This monitoring will cover early prediction of damage, assessment of damage-detection sensors, and inspection guidelines incorporating Non-Destructive Testing (NDT) techniques.
Participants in the Qualify project include representatives from academic institutions, the shipbuilding industry, and classification bodies. The project also welcomes non-participatory ‘Observers’ who represent parties with an interest in the outcome. By inviting observers to engage in steering group meetings twice a year, project participants can source feedback on results, collect requests and input, and hear about the various needs of stakeholders in the maritime industry.
As a participant, Damen plays a pivotal role in the project, producing the joint samples that are then put through the testing process. Damen uses its facilities to produce thick adhesive bond samples in real shipyard conditions to ensure the realism of the testing results. The adhesive is a methyl methacrylate (MMA), which offers a more flexible adhesive bond. Damen’s contribution follows a ‘building block approach’ to form a three layered pyramid:
- Small-scale, laboratory-produced tests intended to ascertain the material properties of the adhesive. These are thin bond tests according to ISO and ASTM standards.
- Mid-scale tests on the joint properties produced by European Adhesive Bonder certified Damen employees. These samples have to be produced in the same manner as they would be for full-scale case study ship testing.
- Full-scale tests for validation in a real-world environment.
The greatest challenge to overcome in this project is to conclusively test the adhesive to a predictable level for up to 25 years, based on experiments that last several months. Adhesive bonding and lightweight materials have each gained widespread adoption by the aerospace and automotive industries, but the shipbuilding industry has almost no existing standard for the application of adhesive bonding. This project performs ground-breaking research into how the adhesive bond behaves with increased thickness, how it degrades under marine conditions, and how it fatigues in operation. The test results must be watertight in order to base industry guidelines upon them.
The adhesive joint is tested and simulated in accelerated ageing and dynamic loading conditions in order to determine adequate tests and tools to rapidly evaluate the performance of adhesive joints for maritime applications.
Tests are conducted at TU Delft, the University of Gent, the University of Cambridge and Knowledge Centre WMC – a testing facility for windmill blades in the north of The Netherlands.
At its halfway stage the project has already yielded some encouraging results. The actual loading conditions of the DAMEN Case study have been defined by International classification society Bureau Veritas using their VeriSTAR Hull and HOMER hydro-structure software. Bureau Veritas performed a simulation of the behaviour of the hybrid ship in all possibly encountered wave conditions to assess the resulting load on 10mm adhesive joints. The simulations run so far have yielded promising results in terms of the effect of fatigue and static load requirements on the joints.
As a project participant, Damen is keen to invest in the future of its manufacturing – and provide the best opportunities to its clients. The potential for constructing hybrid ships with a lightweight superstructure is very promising, and one Damen can see bringing huge benefits to the marine industry.
The current status of the Qualify project is ongoing. Participants are now involved in designing a demonstration product for use in testing this summer, to be validated in 2019. If you’d like to find out more progress details and follow the project more closely, go to the Qualify project website or refer to the M2i website, which can also provide further information.