The Use of Composites for the Hyperloop Tube

Hyperloop tubes make up a large part of the total hyperloop infrastructure. The tubes need to be strong, stiff, durable and airtight. Furthermore, the tube should be able to cope with all the external influences such as saline air, rain, heat and vandalism. Since the tubes make up such a big part of the hyperloop system cost (over 20%, see A Closer Look at Infrastructure Costs), it is desired to achieve these requirements for the lowest cost possible. Steel has been nominated as the material for a hyperloop tube by the hyperloop community but without much consideration. Delft Hyperloop and Jules Dock joined forces to investigate the composite potential for a hyperloop tube.

Since the hyperloop revolution has been started by Elon Musk, steel is seen as the material for the hyperloop tubes. Steel is a widely used and produced material with relatively low costs and high stiffness. Steel is a reliable material that comes in certain strength classes. Because of its frequent use in many different industries for well over a century, knowledge about steel is extensive which makes any design using steel rather easy. Since a hyperloop network mostly consist of tubes, reducing the building time and construction costs will significantly improve the economic potential of a hyperloop system as well as the flexibility and growth potential. It is easy to choose steel as the material for the tubes because it is ready and off-the-shelf. However, looking ahead, there might be other, less commonly used materials that are superior for the construction of hyperloop tubes compared to steel. Examples of companies that are looking into new materials are Hyperloop Transportation Technologies, that plan on using the material vibranium, and Jules Dock, that investigates the composite potential for a hyperloop tube.

As stated before, the focus so far in the hyperloop community has been on steel tubes, possibly in combination with concrete.  However, many innovations in the field of material science have happened over the past decade.  Composite materials have been proven to be a great alternative to conventional metal in several industries, most noticeable in aerospace applications and rapidly emerging in civil structures. Jules Dock, a composite company based in Rotterdam, the Netherlands, is currently developing a new concept for sea-based windmills. These windmills must cope with enormous forces and moments, and therefore usually consist of steel towers that easily reach 100 meter above sea level. Jules Dock has the radical idea to change from steel towers to composite towers.  Their Research & Development department is actively working on the engineering challenges of this concept. They have a lot of expertise in the application composite materials and have recently tested a scale-model of their composite tower concept with promising results.

Jules Dock is planning to use the continuous filament winding technique (CFW) for the lay-up of the composite windings. This is a technique where the windings are laid up continuously over a cylindrical band. Jules dock is actively improving this technique to be able to produce the windmill tower out of one piece. In this way, no welds or bolted connections are required leaving the structure with less failure-critical high-stress locations.

Composites have multiple structural advantages compared to steel. For instance, composite materials are relatively lightweight compared to steel. This means that hyperloop tubes can be lighter and still meet the structural requirements. Furthermore, the composite tubes will have to become thicker than steel tubes. An increased wall thickness has the structural benefit of being less prone to buckling mechanisms. Lastly, due to the lower sensitivity to temperature changes, the composite tubes will also have fewer problems regarding heat expansion.

Aside from the structural advantages, composite tubes also provide interesting production methods. For instance, the continuous filament winding process offers great potential for the production of hyperloop tubes. With this method, large tube sections can be produced at once, leaving the structure with less connecting elements. Furthermore, this winding process offers the possibility to function as a pop-up factory. This would enable the composite tubes to be produced on-site which will remove the logistical challenge of moving large tubes to their locations.

Lastly, composite tubes have several financial advantages. Even though the price for composites is higher than that from steel, composites have the potential of lowering the investments cost. This is mainly due to the lower amount of material that is required. Furthermore, the opportunity to produce the composite tubes on site can allow for cost reduction in the logistics process.

Delft Hyperloop will continue performing a more thorough material research to be able to make a proper trade-off for the hyperloop tube material. Together with Jules Dock, the possibility for composites tubes will be further investigated. In the upcoming months, a concept design will be developed to see if composites are indeed a feasible option. When possible, a prototype of the design will be constructed to evaluate the potential of CFW and to validate the models used for designing.

For more information about Jules Dock, visit https://julesdock.nl/

By Delft Hyperloop and Jules Dock, April 2019