4D printing is a technology that has been the subject of a lot of research lately. Just this week, a team of Dartmouth College researchers developed a smart 3D printable ink that can change shape and color, and they’re far from the only ones doing novel things with 4D printing technology. Suong Van Hoa, a professor in the Department of Mechanical, Industrial and Aerospace Engineering department at Concordia University, is using 4D printing to create composite materials that curve by themselves, eliminating the need for molds.
Suong Van Hoa
“4D printing allows us to make curved composite structures without the need to make curved moulds,” said Hoa. “My main finding is that one can make curved composite pieces — long continuous fibres that have high mechanical properties — more quickly and economically.”
Normally, several steps are required in manufacturing a part like a composite leaf spring, a lightweight shock absorber in vehicles. To make a S-shaped piece, an S-shaped mold would need to be made out of a solid material like metal. Then a reinforcing fabric, pre-impregnated with a resin system, would be laid on the mold to create a composite piece. But with 4D printing, said Hoa, the initial step of building the complex mold could be skipped.
“4D printing of composites utilizes the shrinkage of the matrix resin, and the difference in coefficients of thermal contraction of layers with different fibre orientations to activate the change in shape upon curing and cooling,” he said. “This behaviour can be used to make parts with curved geometries without the need for a complex mould. As such, manufacturing of pieces of curved shapes can be fast and economical. However, the degree of shape-changing depends on the material properties, the fibre orientation, the lay-up sequence and the manufacturing process.”
Part of Hoa’s research involved reconsidering the anisotropic properties of composite layers. Anisotropy is the way a material behaves while bearing loads along different axes. A material’s anisotropic properties are a measure of how it can change in relationship to other factors. For example, resin shrinkage can cause materials to be deformed, or temperature changes can cause fibers to expand or contract. According to Hoa, understanding and controlling for these changes is key to making curved laminates without curved molds.
“Anisotropic properties have been looked at as a liability in the past,” he said. “Now I look at them as an asset.”
Hoa believes that the technology can be applied to fields such as aerospace, among others.
“Another application is for space structures like satellites, where the structures are subjected to extreme temperature fluctuation,” he said. “The structure can open up during the day (when the temperature is high) to collect the solar energy, and close up at night to provide protection for its interiors.”
Last year, Hoa became the first Canadian to be named a fellow of the American Society for Composites for his “outstanding contributions to the composites community through research, practice, education and service.” His research has been published in a paper entitled “Factors affecting the properties of composites made by 4D printing (mouldless composites manufacturing),” which you can access here.
[Source: Concordia University]