Kinked crack paths in polycarbonate samples printed by fused deposition modelling using criss-cross patterns

Additive manufacturing is unquestionably gaining importance in industry. Due to the layer by layer deposit process, it usually leads to an anisotropic material. A question of importance is whether Linear Elastic Fracture Mechanics can be used to assess their resistance to fracture. In this paper, we investigate this point on polycarbonate printed by Fused Deposition Modelling focusing on a criss-crossed deposit pattern. Thanks to tensile and fracture experiments instrumented by Digital Image Correlation, the material is evidenced to be linear elastic until fracture, nearly isotropic in the 2D printing plane but with a strong fracture anisotropy, leading to systematic crack kinking along the weakest plane. The Stress Intensity Factors evolution is measured across the kink and shown to be in agreement with Amestoy-Leblond’s formula. The fracture toughness is observed to be larger than the bulk value, in agreement with irreversible damage and plasticity that are clearly observable at the scale of the threads.