Concordia University professor and engineer Suong Van Hoa has developed a quicker 4-D printing method for manufacturing composite materials. In regular 4-D printing, one creates objects with a 3-D printer that change shape over time once they’re removed from the printer. The fourth dimension is an activation mechanism such as heat, light, magnetic field or absorption of moisture.

However, Van Hoa’s new method of 4-D printing of composites is different from regular 4-D printing. The materials used are stronger, stiffer, and lighter, like those found in the aerospace industry.

“4-D printing allows us to make curved composite structures without the need to make curved molds,” says Suong Van Hoa, professor in the Department of Mechanical, Industrial and Aerospace Engineering in Concordia’s Faculty of Engineering and Computer Science (ENCS). “My main finding is that one can make curved composite pieces — long continuous fibers that have high mechanical properties — more quickly and economically.”

To put the process in perspective, Hoa uses the manufacture a composite leaf spring, a lightweight shock absorber in vehicles as an example. To make an s-shaped piece for a leaf spring, an s-shaped mold would need to be made out of a solid material like metal. Then, a reinforcing fabric that is pre-impregnated with a resin system would be laid upon the mold to make the composite piece.

But that first step – building a complex mold – could be skipped to save time and money, says Hoa, who’s the founding director of Concordia’s Centre for Composites (CONCOM). His findings show how the manufacturing process can be significantly streamlined.

“4-D printing of composites utilizes the shrinkage of the matrix resin, and the difference in coefficients of thermal contraction of layers with different fiber orientations to activate the change in shape upon curing and cooling,” he says. “This behavior can be used to make parts with curved geometries without the need for a complex mold. 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 fiber orientation, the lay-up sequence and the manufacturing process.”

In his paper for Advanced Manufacturing: Polymer & Composites Science, Hoa outlines the anisotropic properties at play in building a composite structure.

For example, resin shrinkage can cause materials to be deformed. Or, temperature changes can cause fibers to expand or contract. Understanding and controlling for these changes is key to making curved laminates without curved molds, Hoa argues.