Abstract
3D printing - or additive manufacturing - has been transitioning from demonstrative prototypes to functional products that are impacting a wide variety of sectors: from biomedical, electronic, and automotive, to aerospace industries. However, the reduced fracture performance often observed in 3D printed parts limits their applications to end-use, load-bearing components. The layered additive deposition process in 3D printing leads to anisotropic fracture behaviors and complicated crack propagation patterns, which brings challenges in computational modeling and analysis. In this study, both extended finite element method (XFEM) and phase-field fracture method (PFFM) are developed to model anisotropic fractures in 3D printed polymers as well as patterned structures for enhanced fracture resistance. The XFEM with cohesive zone method is first developed to model the inter-laminar fracture, cross-laminar fracture, and mixed inter-/cross-laminar fracture of 3D printed samples made of acrylonitrile-butadiene-styrene materials with various build orientations. The model embeds anisotropic weak planes to capture kinked crack propagations and zig-zag crack paths observed in experiments. It is also applied to model anisotropic fracture in shales affected by bedding angles and sedimentary particles. Finally, an anisotropic PFFM formulation is developed to predict complicated crack deflections in 3D printed patterned structures coupled with material anisotropies. The computational simulation of such a fracture is complex, but with the help of PFFM, the process is promising. Indeed, in PFFM, discontinuities are not considered by sharp cracks; instead, they are estimated as thin damage bands. Hence, PFFM can model intricate crack patterns like branching, merging, and deflecting around surface patterns. However, PFFMs for anisotropic fracture, mostly using a simple quadratic degradation function without any user-defined parameters, provide solutions that are sensitive to a length scale (that controls the width of the damage band). From this perspective, PFFMs with considering the CZM and softening behavior for anisotropic behavior of 3D printed composite are capable of delivering the insensitive solution to the length scale parameter. This research introduces a length scale insensitive PFFM for anisotropic fracture of 3Dprinted polymers considering the cohesive zone model with softening behavior of anisotropy which is induced by oriented layers. This study sheds light on predicting fractures in 3D printed materials and structures with optimal build and topology designs for enhanced performance.