New meta-crystal materials have superior strength to uniform 3D printed lattices

A joint team of researchers from the University of Sheffield and Imperial College London have developed a new family of 3D printed metamaterials: meta-crystal materials. The new materials integrate a novel lattice composition that mimics the structure of polycrystalline microstructures.

Additive manufacturing is opening up a ton of new potentials in the creation of metamaterials, as it enables the production of complex internal geometries, which themselves impart specific properties and characteristics into parts. These potentials, however, have not been exhausted yet.

That is, while lattice structures are commonly integrated into 3D printed structures to decrease weight while providing a certain degree of strength, many of the patterns generated have a uniform layout, meaning that all nodes in the lattice conform to a regular array with struts between nodes all following common planes.

The uniform structure of lattices are inspired by the structure of a metallic single crystal. As the researchers explain in their study, the nodes in the lattice are equivalent to the atoms in the single crystal and the struts mimic the atomic bonds. Though these types of lattices can perform well, they do come with their limitations, mainly in regards to mechanical performance.

A 3D printed part with a uniform lattice geometry is susceptible to deformation when put under compression, as the lattice can shear along one or more of the planes of the nodes. “With nothing to inhibit this shearing,” the researchers write, “the collapse becomes catastrophic.”

By mimicking the structure of polycrystalline materials, however, the researchers have found a solution to this challenge. In polycrystalline materials, the alignment of the atomic planes is completely random, so when a shear force is applied in a particular direction, the crack or breakage is slowed or even stopped when it reaches a crystal where the atoms are aligned differently from the cracked crystal. With polycrystalline materials it is also possible to introduce different materials in the form of phases, precipitates or inclusions, which can strengthen the materials more.

Based on this metallurgic insight, Professor Iain Todd from the Department of Materials Science and Engineering at the University of Sheffield and his colleagues began to develop 3D printable lattice structures that mimic polycrystalline microstructures and thus provide better strength and damage resistance than parts with a uniform lattice.

“This approach to materials development has potentially far-reaching implications for the additive manufacturing sector,” said Professor Todd. “The fusion of physical metallurgy with architected meta-materials will allow engineers to create damage-tolerant architected materials with desired strength and toughness, while also improving the performance of architected materials in response to external loads. And while these materials can be used as standalone structures, they can also be infiltrated with other materials in order to create composites for a wide variety of applications.”

Adapting the polycrystalline microstructures into a printable lattice structure involved computer modeling atomic structures, scaling them up and creating meso-structures based on them. The new materials, aptly called meta-crystals, provide a new and innovative model for how next-gen materials can be conceived and developed.

In their study, the researchers 3D printed a series of test parts which integrate the meta-crystal structure. These parts reportedly performed well in tests, demonstrating their energy absorbency and strength. In fact, the meta-crystal components was able to withstand almost seven times the energy that single-crystal-inspired lattices were.

Dr Minh-Son Pham of Imperial College London added: “This meta-crystal approach could be combined with recent advances in multi-material 3D printing to open up a new frontier of research in developing new advanced materials that are lightweight and mechanically robust, with the potential to advance future low carbon technologies.”

A study detailing the research was recently published in the journal Nature.