RMIT University
PhD candidate Jordan Noronha holding a sample of the new titanium lattice structure 3D printed in cube form.
RMIT University has announced that a team of researchers have created a new metamaterial, a term used to describe an artificial material with unique properties not observed in nature, from common titanium alloy, to be used 3D printing.
The university, which has three campuses and two sites in Australia, as well as two campuses in Vietnam and an industry collaboration centre in Spain, claims that a 3D printed ‘metamaterial’ boasting levels of strength for weight not normally seen in nature or manufacturing, could change ‘how we make everything’.
The team says that tests show that the material’s lattice structure design show that it is 50% stronger than the next strongest alloy of similar density used in aerospace applications.
RMIT’s Distinguished Professor Ma Qian said that decades of trying to replicate lattice 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.
“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,” said Qian.”
The university says that metal 3D printing provides ‘unprecedented’ innovative solutions to these issues. By pushing 3D printing to its limits, the RMIT team says it optimised a new type of lattice structure to distribute the stress more evenly, which enhances its strength or structural efficiency.
“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 in nature,” said Qian. “By effectively merging two complementary lattice structures to evenly distribute stress, we avoid the weak points where stress normally concentrates.”
The design was 3D printed using laser powder bed fusion (LPBF). The titanium lattice cube was 50% stronger than cast magnesium alloy ME54 according to the team, the strongest alloy of similar density used in aerospace applications. The team says the new structure had effectively halved the amount of stress concentrated on the lattice’s weak points.
RMIT University
Compression testing shows (left) stress concentrations in red and yellow on the hollow strut lattice, while (right) the double lattice structure spreads stress more evenly to avoid hot spots.
The lead author on the study and RMIT PhD candidate Jordan Noronha said that they could make this structure at the scale of several millimetres or several metres in size using different types of printers.
The team says 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 light weight, 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.
While the material is currently resistant to temperatures as high as 350°C, they believe it could be made to withstand temperatures of up to 600°C using more heat resistant titanium alloys, for applications in aerospace or firefighting drones.
“Traditional manufacturing processes are not practical for the fabrication of these intricate metal metamaterials, and not everyone has a laser powder bed fusion machine in their warehouse,” added Noronha.
Noronha continued: “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.”
Technical Director of RMIT’s Advanced Manufacturing Precinct, Distinguished Professor Milan Brandt, said the team welcomed companies wanting to collaborate on the potential applications.
Brandt said: “Our approach is to identify challenges and create opportunities through collaborative design, knowledge exchange, work-based learning, critical problem-solving and translation of research.”
