Additive manufacturing of compliance optimized variable stiffness composites through short fiber alignment along curvilinear paths

Official URL: https://dx.doi.org/10.1016/j.addma.2020.101728

Short fiber-reinforcement has been used to improve the structural performance of extrusion based 3D printed polymer materials. The converging nozzle preferentially orients the short fibers along the printing direction. By locally steering the print paths to orient the fiber directions, the benefit of the anisotropic fiber reinforcement can be optimized. In this study, a methodology is developed to design and manufacture 3D printed short fiber-reinforced composite materials with optimized fiber or print directions. The standard open-hole tension sample geometry was employed as a test case. The least squares & continuity constraints (LSC) method was used to design the locally varying fiber orientation of each ply/layer to optimize for minimum compliance. An algorithm was developed to convert optimum discrete fiber angles to continuous paths. Material properties were estimated based the measured the fiber orientation tensor in conjunction with the Halpin–Tsai homogenization method. Strain measurements on open-hole tensile specimens by digital image correlation (DIC) were in good agreement with finite element model predictions. Despite some defects at path drop offs, LSC optimized samples showed improved stiffness and strength over zero degree orientation samples. In addition, samples prepared with print paths following streamlines for potential flow over a cylinder yielded higher strength and stiffness.