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Scientists print 3D structure boasting unnatural strength

by Mark Cantrell
Scientists at an Australian university have succeeded in printing a 3D metal structure that demonstrates preternatural strength.

Scientists at an Australian university have succeeded in printing a 3D metal structure that demonstrates preternatural strength.

The titanium alloy lattice ‘meta-material’ – so-called because its boasts levels of strength for weight not normally seen in nature or manufacturing – could change the way everything from medical implants to aircraft or rocket parts are made.

Doubtless, given its properties, it likely will also find application in construction and engineering too.

Writing in the journal, Advanced Materials, the team from RMIT University explain how it is the meta-material’s unique lattice structure design that make it anything but common. Tests are said to show it is 50% stronger than the next strongest alloy of similar density used in aerospace applications.

Lattice structures made from hollow struts were originally inspired by nature: Strong hollow-stemmed plants like the Victoria water lily or the hardy organ pipe coral (Tubipora musica) showed the way in combining lightness and strength.

However, as RMIT’s distinguished professor, Ma Qian explained, decades of trying to replicate these hollow ‘cellular structures’ in metals has been frustrated by the common issues of manufacturability and load stress concentrating on the inside areas of the hollow struts, leading to premature failures.

Qian said: “Ideally, the stress in all complex cellular materials should be evenly spread. However, for most topologies, it is common for less than half of the material to mainly bear the compressive load, while the larger volume of material is structurally insignificant.”

By pushing 3D printing design to its limits, the RMIT team optimised a new type of lattice structure to distribute the stress more evenly, enhancing its strength or 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.”

Laser printer

The team 3D printed this design 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% 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.

The double lattice design also means any cracks are deflected along the structure, further enhancing the toughness.

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.

Noronha said: “Compared with the strongest available cast magnesium alloy currently used in commercial applications requiring high strength and light weight, our titanium meta-material 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.”

The team plans to further refine the material for maximum efficiency and explore applications in higher-temperature environments.

While currently resistant to temperatures as high as 350C, they believe it could be made to withstand temperatures up to 600C using more heat-resistant titanium alloys, for applications in aerospace or firefighting drones.

However, as the technology to make this new material is not yet widely available, its adoption by industry might take some time.

Noronha said: “Traditional manufacturing processes are not practical for the fabrication of these intricate metal meta-materials, and not everyone has a laser powder bed fusion machine in their warehouse.

“However, as the technology develops, it will become more accessible and the printing process will become much faster, enabling a larger audience to implement our high-strength multi-topology metamaterials in their components. Importantly, metal 3D printing allows easy net shape fabrication for real applications.”

Main image: Jordan Noronha holds a sample of the new titanium lattice structure in 3D printed cube form. Credit: RMIT University


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