A simple model for estimating the crack kinking angles of pure shear fracture of 3D printing polymers

Shear fracture studies of three-dimensional (3D) printing polymers with interfaces were rarely reported due to their complicated mechanics and material issues. In this study, a short-beam shear fracture approach was employed to characterize the mode-II shear fracture toughness of polyamide specimens of three printing surface angles made with selective laser sintering (SLS). Results show that a pure shear crack only existed if the initial crack propagated along the printing interface. In other cases, initial cracks kinked right after crack initiation, so no valid shear fracture toughness was measured. A simple model based on linear elastic fracture mechanics including anisotropic fracture toughnesses was proposed to predict the crack kinking angles. The prediction agreed with the measurements well and was more reasonable than the prediction based on the maximum tensile stress criterion.