Using regular titanium alloy, RMIT University researchers have produced a novel metamaterial—a word used to characterise an artificial material with special qualities not found in nature. The strength-to-weight ratio of this 3D-printed “metamaterial” is unparalleled in nature and manufacturing, and it has the potential to transform the production of anything from aircraft parts to medical implants.
The material features a unique lattice structure design, and tests have revealed that its shape makes it 50 per cent stronger than the next strongest allow of similar density used in aerospace applications.
The combination of strength and lightness found in robust hollow-stemmed plants like the resilient organ pipe coral (Tubipora musica) and the Victoria water lily served as the original inspiration for these lattice structures composed of hollow struts.
Many organisations have been trying to perfect this design for decades, however, as RMIT’s Distinguished Professor Ma Qian explains, many of them encountered the shared predicament of manufacturability and load tension being focused in the interior regions of the hollow structures.
However, with metal 3D printing technology has now advanced enough to turn this design into a functional reality.
The RMIT team pushed the limits of this technology and managed to optimise a new type of lattice structure that distributes the weight more evenly, enhancing its structural efficiency.
Qian said: “We designed a hollow tubular lattice structure that has a thin band running inside it. These two elements together show strength and lightness never before seen together in nature.
“By effectively merging two complementary lattice structures to evenly distribute stress, we avoid the weak points where stress normally concentrates.”
The team 3D printed this design at RMIT’s Advanced Manufacturing Precinct using a process called laser powder bed fusion, where layers of metal powder are melted into place using a high-powered laser beam.
Testing showed the printed design — a titanium lattice cube — was 50 per cent stronger than cast magnesium alloy WE54, the strongest alloy of similar density used in aerospace applications.
The new structure had effectively halved the amount of stress concentrated on the lattice’s infamous weak points.
Study lead author and RMIT PhD candidate Jordan Noronha said they could make this structure at the scale of several millimetres or several metres in size using different types of printers.
This printability, along with the strength, biocompatibility, corrosion and heat resistance make it a promising candidate for many applications from medical devices such as bone implants to aircraft or rocket parts.
“Compared with the strongest available cast magnesium alloy currently used in commercial applications requiring high strength and lightweight, our titanium metamaterial with a comparable density was shown to be much stronger or less susceptible to permanent shape change under compressive loading, not to mention more feasible to manufacture,” said Noronha.
The team plans to continue refining the material for maximum efficiency and explore applications in higher-temperature environments.
While currently resistant to temperatures as high as 350 degrees Celsius, they believe it could be made to withstand temperatures up to 600 degrees Celsius using more heat-resistant titanium alloys, for applications in aerospace or firefighting drones.
The project was funded by the Australian Research Council.
