New 3D Printing Technique Produces High-Performance Composites
A team of researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (Seas) has demonstrated a novel 3D printing method that yields unprecedented control of the arrangement of short fibers embedded in polymer matrices. They used this additive manufacturing technique to program fiber orientation within epoxy composites in specified locations, enabling the creation of structural materials that are optimized for strength, stiffness, and damage tolerance.
Nature has produced exquisite composite materials — wood, bone, teeth, and shells, for example — that combine light weight and density with desirable mechanical properties such as stiffness, strength and damage tolerance.
Since ancient civilizations first combined straw and mud to form bricks, people have fabricated engineered composites of increasing performance and complexity. But reproducing the exceptional mechanical properties and complex microstructures found in nature has been challenging.
Rotational 3D Printing
The newly developed method by Harvard scientists, referred to as “rotational 3D printing,” could have broad ranging applications. Given the modular nature of their ink designs, many different filler and matrix combinations can be implemented to tailor electrical, optical, or thermal properties of the printed objects. The scientist can now pattern materials in a hierarchical manner, akin to the way that nature builds.
The work, described in the journal PNAS, was carried out in the Lewis lab at Harvard. Collaborators included then-postdoctoral fellows Brett Compton (now Assistant Professor in Mechanical Engineering at the University of Tennessee, Knoxville), and Jordan Raney (now Assistant Professor of Mechanical Engineering and Applied Mechanics at the University of Pennsylvania); and visiting PhD student Jochen Mueller from Prof. Kristina Shea’s lab at ETH Zurich.
According to Compton, Rotational 3D printing can be used to achieve optimal, or near optimal, fiber arrangements at every location in the printed part, resulting in higher strength and stiffness with less material. Rather than using magnetic or electric fields to orient fibers, the developers control the flow of the viscous ink itself to impart the desired fiber orientation.
3D Printing of Engineered Materials
Compton noted that the team’s nozzle concept could be used on any material extrusion printing method, from fused filament fabrication, to direct ink writing, to large-scale thermoplastic additive manufacturing, and with any filler material, from carbon and glass fibers to metallic or ceramic whiskers and platelets.
The technique allows for the 3D printing of engineered materials that can be spatially programmed to achieve specific performance goals. For example, the orientation of the fibers can be locally optimized to increase the damage tolerance at locations that would be expected to undergo the highest stress during loading, hardening potential failure points. More control over structure means more control over the resulting properties, which vastly expands the design space that can be exploited to optimize properties further.
This article was first published by Laborpraxis Worldwide.
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