Nature provides countless examples of perfectly manufactured products – delicate butterfly wings that can transport a creature thousands of miles; Mother of Pearl that provides intricate and strong layers of protection for an oyster; and human bones that fall yet rarely break.
A WSU team has introduced a new, one-step 3D printing approach that could allow manufacturers to approximate not only the design but also the performance of such complex natural materials better than ever before. They report on their work in the journal, Additive Manufacturing.
“Traditionally, it was the properties of the material that determined how they were used,” said Amit Bandyopadhyay, professor in the School of Mechanical and Materials Engineering. “In this case, we used 3D printing to design structural components to enhance performance.”
For generations, engineers have come up with intricate design ideas, but because of their complexity, they had no way to make them. Traditional manufacturing processes are generally limited to simpler geometries. When more intricate designs are possible, they are often too expensive to mass produce.
The advent of 3D printing meant that engineers could finally print any design. The technology has become popular with hobbyists who can print out any desired shape dreamed up on a computer file.
But, while they can print out beautiful designs, achieving the performance of a complex butterfly wing or a human bone has remained out of reach. When researchers have tried to create components using calcium phosphate — the very same materials that bones or shells are made of — they have failed.
“They’re terrible — they break so easily,” said Bandyopadhyay. “But shells are amazing. The performance is very different because of the architecture and stacking of materials.”
So, for instance, bones can be damaged without breaking because mineral platelets slide against one other, which prevents them from failing. In abalone shells, mineral bridges act like cement to allow a change of shape and load transfer between cell fragments, creating a strong and tough microstructure. Nature uses variation in composition and architecture within a single component to create structures that are optimized for their environment.
In their work, the WSU researchers were able to customize the performance of a component by printing and layering two different classes of materials, ceramic and metal, in a one-step process — a feat that would be difficult to achieve using traditional manufacturing. The researchers used laser processing to transition in a gradual way from metal to ceramic and back to metal, producing a layered, ribbon-like structure that approaches natural materials. Because the materials transitioned gradually from one layer to the next, the composites didn’t suffer from the cracks and brittleness that normally plague such pieces.
“The main significance is that we can go from different classes of material in one step,” said Kellen Traxel, lead author on the paper and a graduate student in the School of Mechanical and Materials Engineering. “It was pretty exciting.”
“People have talked about and analyzed the natural structures of bio-inspired materials,” said Bandyopadhyay, “but we have taken that knowledge and applied it in design.”
The researchers tested the components they developed and showed they could tailor their structure for desired thermal and mechanical performance. They worked initially with titanium and the ceramic, niobium-carbide, but they are now experimenting with designs using different metal/ceramic mixtures.
The work could be applied to numerous applications from ballistic armor design to metallic hip implants.
“How can we leverage this work to make structures that have not been possible?” said Traxel. “We have advanced the state-of-the-art with this technology and laid a foundation. I hope we can inspire ingenuity.”
“That’s what is driving inspiration in the 3D printing world,” he said. “What we think of as impossible is starting to be feasible.”
For his part, Bandyopadhyay and his colleagues in the W. M. Keck Biomedical Materials Research Laboratory have been involved in 3D printing research since the 1990s and began 3D printing of metal materials in the early 2000s.
“For the last 20 to 30 years, we have talked about this, but the performance variation that we showed is real,” he said. “We can dream of a lot of applications.”
This research was funded by the National Science Foundation and the National Institutes of Health.