3D Printed Titanium Lattice Floats Even After Severe Damage

Australian engineers have developed a strong, lightweight titanium metamaterial that remains buoyant after sustaining major structural damage. The 3D printed material could support future marine infrastructure, including buoys, jetties and floating sensors.

Foam-Filled Titanium Struts

Researchers at RMIT University created the open-cell lattice from hollow, interconnected titanium struts. Although metal lattices can have extremely low overall densities, their open spaces usually fill with water. As a result, they sink despite their lightweight construction.

The team addressed this problem by filling only the hollow struts with polyurethane foam. Water can still flow freely through the lattice’s external openings. However, tiny sealed cells inside the foam trap gas and prevent water from entering the struts.

Samples remained afloat in freshwater for more than two months. According to the researchers, the study presents the first reported floating metal–polymer open-cell hybrid lattice metamaterial.

A New Way To Measure Density

The researchers also introduced the concept of ‘skeletal density’ to predict whether an open structure will float. Conventional density calculations include the empty spaces within a lattice, even though these spaces can fill with water and do not provide buoyancy.

Skeletal density considers only the parts that keep water out: the titanium walls and sealed foam-filled channels. If this density is lower than that of the surrounding liquid, the open structure should remain buoyant.

Strong And Damage-Resistant

At the same overall density, the hybrid titanium lattice was 70% stronger than the stainless steel or high-density polyethylene commonly used for marine applications.

Short-term corrosion tests also produced promising results. After two weeks in natural seawater from Melbourne’s Port Phillip Bay, the material lost 0.15% of its mass, while its strength decreased by less than 1%. Further testing will be necessary to assess its long-term behaviour in marine environments.

The lattice continued to float after cracking, failure at important connection points and the fracture of an entire structural layer. It sank only after researchers severely crushed and compacted it. This distributed buoyancy could offer an advantage over conventional hollow structures, which may quickly flood when their outer casing cracks.

From Buoys To Thermal Management

A prototype 3D printed buoy remained stable in a turbulent seawater tank tilted by up to 45 degrees. It required no sealed outer casing, protective coating or additional flotation component.

The researchers now plan to scale up the prototypes and test them under realistic marine and deep-sea conditions. They also suggest that changing the filling inside the titanium framework could adapt similar structures for energy absorption, thermal management and vibration control.

RMIT University led the project with the Conservatoire National des Arts et Métiers in France. The study appeared in Advanced Materials.

Source: RMIT University
Photos: Sara Tan / RMIT