Using a mix of fibre-reinforced epoxy-based thermosetting resins and 3D extrusion printing techniques, scientists at Harvard and the Wyss Institute have developed cellular composite materials of unprecedented light weight and stiffness.
Until now, 3D printing has been developed for thermo plastics and UV-curable resins—materials that are not typically considered as engineering solutions for structural applications. By moving into new classes of materials like epoxies, it opens up new avenues for using 3D printing to construct lightweight architectures, broadening the materials palette for 3D printing.
Lewis and Brett G. Compton, a former postdoctoral fellow in her group, developed inks of epoxy resins, spiked with viscosity-enhancing nanoclay platelets and a compound called dimethyl methylphosphonate, and then added two types of fillers: tiny silicon carbide “whiskers” and discrete carbon fibres. Key to the versatility of the resulting fibre-filled inks is the ability to control the orientation of the fillers.
Lorna Gibson, a professor of materials science and mechanical engineering at the Massachusetts Institute of Technology said;
This paper demonstrates, for the first time, 3D printing of honeycombs with fibre-reinforced cell walls, of particular significance is the way that the fibres can be aligned, through control of the fibre aspect ratio—the length relative to the diameter—and the nozzle diameter. This marks an important step forward in designing engineering materials that mimic wood, long known for its remarkable mechanical properties for its weight.
The direction that the fillers are deposited controls the strength of the materials, Lewis and Compton have shown that their technique yields cellular composites that are as stiff as wood, 10 to 20 times stiffer than commercial 3D-printed polymers, and twice as strong as the best printed polymer composites. The ability to control the alignment of the fillers means that fabricators can digitally integrate the composition, stiffness, and toughness of an object with its design.
The work could have applications in many fields, including the automotive industry where lighter materials hold the key to achieving aggressive government-mandated fuel economy standards. According to one estimate, shedding 110 pounds from each of the 1 billion cars on the road worldwide could produce $40 billion in annual fuel savings.
3D printing has the potential to radically change manufacturing in other ways too. Lewis says the next step will be to test the use of thermosetting resins to create different kinds of architectures, especially by exploiting the technique of blending fillers and precisely aligning them. This could lead to advances not only in structural materials, but also in conductive composites.