Engineers at RMIT University say they have developed a 3D-printed titanium material that can float in water even after sustaining significant damage, a result they argue could inform future marine infrastructure designs.
The research describes a titanium lattice made of hollow, interconnected struts that are filled with polyurethane foam. RMIT said the approach allows water to flow through the structure while maintaining buoyancy, addressing a long-standing issue with lightweight metal lattices that can sink once water enters their open internal spaces.
Lead researcher Dr Jordan Noronha from RMIT’s Centre for Additive Manufacturing said the team’s design targets that limitation by sealing buoyant elements within the structure rather than enclosing the whole component. “By filling only the hollow titanium struts with polyurethane foam, we created a structure that allows water to flow through it while remaining buoyant even after significant cracking and damage,” Noronha said.
RMIT said the work is the first reported demonstration of what it describes as a “floating metal-hybrid lattice metamaterial”. The university said buoyancy was validated by samples that floated in freshwater for more than two months.
To guide design, the researchers introduced what they call “skeletal density” — a measure intended to better predict whether an open lattice will float. RMIT said conventional density calculations treat the lattice’s open internal space as part of the structure, even though water can occupy that space and therefore does not contribute to buoyancy. The skeletal density approach instead accounts only for the parts that exclude water, including titanium walls and sealed, foam-filled channels. “This gives engineers a simple design rule: if the skeletal density is lower than that of the surrounding liquid, the structure will float – even when water flows through all its external openings,” Noronha said.
In mechanical testing, RMIT said the titanium structure was 70% stronger than stainless steel or high-density polyethylene used in marine applications, when compared at the same overall density. The material was also subjected to short-term corrosion testing using natural seawater from Melbourne’s Port Phillip Bay, with RMIT reporting a 0.15% mass loss after two weeks of immersion and a strength decline of less than 1%.
The hybrid lattice remained buoyant after damage including cracking, failure at connection points and fracture of an entire lattice layer, according to RMIT. It reportedly sank only after being severely crushed and compacted. Noronha attributed the damage tolerance to sealed gas cells in the foam that prevent water from flooding the hollow struts, in contrast to conventional hollow marine structures that can fill with water after cracking.
RMIT said the team demonstrated the concept with a 3D-printed buoy that remained stable in a turbulent seawater tank rotated up to 45 degrees, without a sealed casing, protective coating or additional flotation.
Project leader Distinguished Professor Ma Qian said the group’s next steps include scaling up demonstration parts and testing performance over the long term under realistic marine and deep-sea conditions. He said the structure could also be adapted for uses beyond marine infrastructure by changing the material inside the titanium framework, including energy absorption, thermal management and vibration control.
The project was led by RMIT’s Centre for Additive Manufacturing in collaboration with the Conservatoire National des Arts et Métiers in France. The Australian Research Council and RMIT’s School of Engineering supported the research.
The study, titled “Breaking the surface: buoyant metal–polymer open–cell hybrid lattice metamaterials”, was published in Advanced Materials (DOI: 10.1002/adma.74641).
