Three-dimensional printing of biomimetic variable stiffness composites with controlled orientations and volume fraction of fibers

In this paper, biomimetic continuous fiber reinforced composite structures were modeled and printed on the basis of variable distributions of fiber orientation and the fiber volume fraction, which are similar to the wood structure in the vicinity of a knot. The variable distributions of curved fibers in the variable stiffness composites (VSCs) without gaps and overlaps were realized during the 3D printing process by the control of positioning a nozzle and the adaptive feed of plastic. To demonstrate efficiency of the modeling method and the 3D printing process, a VSC plate with a hole under tensile loading was designed, printed and tested. The results of tensile tests showed that the main failure of the composite plates occurs far from the hole. Furthermore, numerical and experimental strain fields obtained by the finite element method and digital image correlation, respectively, are similar. The efficiency in fiber savings for the composite plates was improved by the change in reinforcement from unidirectional fibers to curved fibers adapted to heterogeneous stress fields.