Effects of Angular Corners on Short Fiber Orientation and Mechanical Integrity in Extrusion 3D Printing

Angular paths and corners are common in toolpaths in material extrusion additive manufacturing and could affect shear and material flow. This study focuses on 3D printed corners by using short fibre reinforced materials regarding the fibre orientation and mechanics. 3D fibre orientation tensor at different turn angles (30°-150°) was measured, and main-axis alignment was low when it turned orthogonally, while out-of-plane alignment increased with the angles. The fibre orientation closely links to mechanical properties. Tensile tests showed decreasing response force with increasing turn angles, and failure was attributed to fibre pull-out, fibre displacement, and matrix plastic deformation. We built 2D finite-element models of the 150° corner with the composite Hashin damage criterion and energy-based damage evolution law, in order to simulate large deformation failure model. The mechanical simulation successfully captured important features of specimen fracture due to crack initiation and propagation, which agreed with the experiment. Finally, cyclic tensile of displacement-controlled modes showed fast mechanical degradation of the sharp corners (greater turn angles) and compliance of smaller turn angles. This study highlights the variation of fibre orientation and mechanical weakness at corners, especially for sharp corners. It may enlighten design strategies (e.g. lattices with angular corners) to control fibre orientation and avoid mechanical weakness.