چكيده به لاتين
Mechanical components produced by additive manufacturing methods often have small defects in their structures by nature. More specifically for biomaterials, the possibility of crack initiation and growth can be high considering their loading conditions. As a result, additively manufactured biomaterials can be very susceptible to fracture. Therefore, knowing the fracture behavior of these materials can increase the applicability of additive manufacturing. In this thesis, the effect of printing orientation on the mechanical properties of polycarbonate parts produced by the Fused Deposition Modelling (FDM) is investigated. To do so, tensile, flexural, mode I and mixed mode I/II fracture tests were performed. The results show that the tensile, flexural and fracture behavior of the FDM parts are anisotropic; although the anisotropy of fracture toughness in in-plane printed specimens is lower than that of the other characteristics. Moreover, it is shown that the material can be considered isotropic regarding its elastic modulus. For parts with in-plane printing orientations, the ultimate tensile strength and fracture toughness of the samples produced in different printing directions are in the range of 40-53 MPa and 1.93-2.37 MPa.m1/2, respectively. This means that compared to the strongest direction, the weaker one has 25% less tensile strength and 19% less resistance to crack growth. For the parts printed in the out-of-plane direction, the difference in fracture toughness for different directions goes up to 50%, in some cases being higher than the fracture toughness of the bulk material. Additionally, after investigating the mixed mode I/II fracture behavior of the material, the generalized maximum tangential stress (GMTS) criterion is shown to be able to predict well the trends in the experimental data. By using this criterion and considering the observed fracture paths, three fracture mechanisms of: inter-layer fracture, cross-layer fracture and crack multi-kinking are proposed and a method is suggested to predict the fracture loads based on these fracture mechanisms.
