Design of a continuous fiber trajectory for 4D printing of thermally stimulated composite structures

Deformation control of 4D printing has always been challenging. Herein, a design method for the fiber trajectory for 4D printing composite structures with embedded continuous fibers is reported, wherein the designed composite structures can be deformed into many types of deployable surfaces. Deformation of the bilayer composite structure was driven by differences in the coefficients of thermal expansion (CTEs) between the resin substrate and embedded fibers. The bending curvature and direction of the composite structure is controlled by adjusting fiber orientations. According to differential geometry theory, the relationship between the angle of intersecting fiber bundles and curvature of the final shape was obtained. Therefore, arbitrary deployable surfaces, including conical, cylindrical, and tangent surfaces, can be deformed. This design and additive manufacturing strategy allow precise control of the deforming process, greatly extending the potential applications of 4D printing.