ACTIVE COMPOSITES AND 4D PRINTING

Additive manufacturing, or 3D printing, allows the precise placement of materials at micrometer resolution in a layer-by-layer manner. The recent development of the polyjet techniques admits 3D printing of a solid composed of multiple materials with essentially no or little restrictions on the geometric complexity of their spatial arrangement. Complex 3D solids therefore can be printed with different material distributions in an optimal and controllable fashion, enabling the design and fabrication of parts, devices, and structures with novel multifunctional performance. In this paper, we present the paradigm of printed active composites and 4D printing where the shape of a printed 3D object can change upon external stimuli, thus offering one additional dimension, time, for shape forming and control. We demonstrate this concept by printing shape memory fibers (SMF) in an elastomer matrix to create a composite. After printing, the programing of the SMFs creates time dependence of the composite configuration change. This process has considerable design freedom to enable creation of composites with complex and controllable anisotropic thermomechanical behavior through the fiber architecture design, such as shape, size, orientation and even spatial variation of these parameters. We design and print laminates in thin plate forms that can be programmed to assume complex three-dimensional configurations including bent, coiled, and twisted strips, folded shapes (origami).