Australian engineers at RMIT University have developed a 3D-printed titanium lattice material that floats in water even after severe damage, overcoming a fundamental challenge that has long kept...
Although metallic lattices can be incredibly light – with densities less than one-tenth of water – their open, interconnected spaces allow water to enter, causing them to sink.
To predict whether open structures will float, the research team developed a new measure called skeletal density.
Australian engineers at RMIT University have developed a 3D-printed titanium lattice material that floats in water even after severe damage, overcoming a fundamental challenge that has long kept metallic structures out of marine infrastructure, according to reporting by Marine Technology News.
The material consists of hollow, interconnected titanium struts filled with polyurethane foam. While metallic lattices can be remarkably light with densities less than one-tenth that of water, their open spaces typically allow water to flood in and cause them to sink.
Dr. Jordan Noronha, lead researcher from RMIT’s Centre for Additive Manufacturing, explained the mechanics of the design to Marine Technology News.
Although metallic lattices can be incredibly light – with densities less than one-tenth of water – their open, interconnected spaces allow water to enter, causing them to sink. This has made these strong, lightweight structures unsuitable for marine infrastructure – until now. 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.
Dr. Jordan Noronha, RMIT University
Engineering Metrics and Skeletal Density
To predict whether open structures will float, the research team developed a new measure called skeletal density. Conventional density calculations factor in all open spaces within a lattice, even though water ultimately occupies those areas and fails to contribute to buoyancy.
Skeletal density considers strictly the parts of the structure that exclude water, specifically the 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.
Dr. Jordan Noronha, RMIT University
Validation for the design came through testing samples in freshwater for more than two months. Comparative testing showed the titanium lattice was 70% stronger than the stainless steel or high-density polyethylene currently used in jetties, buoys, and floating sensors when evaluated at the same overall density. Short-term corrosion testing using natural seawater from Melbourne’s Port Phillip Bay revealed that after two weeks of immersion, the lattice lost just 0.15% of its mass while its strength declined by less than 1%.
Damage Tolerance and Practical Applications
The hybrid material maintains buoyancy even after sustaining heavy damage. According to Marine Technology News, testing demonstrated that the structure survived cracking, key connection point failures, and the complete fracture of an entire lattice layer. It sank only after being severely crushed and compacted.
Tiny, sealed cells in the foam trap gas and prevent water from flooding the hollow struts. In this way the foam acts as a distributed barrier that helps the structure remain afloat after damage – unlike conventional hollow marine structures, which can rapidly fill with water after cracking.
Photo: marinelink.com
Dr. Jordan Noronha, RMIT University
The team demonstrated the technology by building a 3D-printed marine buoy that remained stable in a turbulent seawater tank rotated up to 45 degrees, functioning without a sealed casing, extra flotation, or protective coatings.
Project leader Distinguished Professor Ma Qian noted that the RMIT Centre for Additive Manufacturing collaborated with the Conservatoire National des Arts et Métiers in France on the project. Next steps involve scaling up demonstration parts and testing long-term performance under realistic marine and deep-sea conditions. Researchers also plan to explore alternative internal materials to tailor the structure for energy absorption, thermal management, and vibration control.
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