RMIT titanium lattice prototype stays afloat after major damage

A 3D-printed buoy remains stable in a turbulent seawater tank as the test system rotates up to 45 degrees. It keeps floating without a sealed casing, protective coating or extra flotation. The prototype comes from RMIT University's Centre for Additive Manufacturing, where researchers have built a titanium lattice that remains buoyant even after severe damage.

The obstacle was water. Metal lattices can be very light because their struts are hollow and interconnected, but their open spaces also let water enter. RMIT's solution fills only those hollow titanium struts with polyurethane foam. Tiny sealed cells in the foam trap gas and form a distributed barrier, while water can continue flowing through the lattice's external openings.

The researchers say the study is the first reported demonstration of a floating metal-polymer open-cell hybrid lattice metamaterial. They developed a design measure called skeletal density, which counts the titanium walls and sealed, foam-filled channels but excludes open space that water can occupy. Their rule is simple: when skeletal density is lower than that of the surrounding liquid, the open structure floats.

The results point to a potential material for marine applications. At the same overall density, the titanium lattice was 70% stronger than stainless steel or high-density polyethylene. In natural seawater from Melbourne's Port Phillip Bay, it lost only 0.15% of its mass after two weeks, while its strength declined by less than 1%. The structure also stayed afloat after cracking, failures at key connection points and the fracture of an entire lattice layer; it sank only after severe crushing and compaction.

In concrete terms, the work could give buoys, floating sensors and other marine structures a way to combine low weight with damage tolerance, rather than relying on a sealed casing or extra flotation. That remains a prospect, not a deployment: RMIT has demonstrated a 3D-printed prototype, and the team led by Distinguished Professor Ma Qian still plans larger parts and long-term tests in realistic marine and deep-sea conditions. The collaboration includes the Conservatoire National des Arts et Métiers in France.