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• Experimental three-point bending tests in material extruded short beam specimens. • DIC evaluated the field displacement in specimens with different raster orientation. • Detection of neck-shaped defects in knots of grid pattern specimens. In this work, a thorough fracture assessment of additive manufactured specimens made by 3D printed polylactic acid (PLA) under three-point bending is presented. This polymer is widely used in additive manufacturing for numerous applications, gaining prominence in fields such as biomechanics. Prismatic fully dense specimens and lattice structure specimens with different raster orientations and densities were fabricated using the material extrusion-based additive manufacturing technique. The objective is to analyse the effect of relevant process parameters on the fracture mechanism of short beam specimens tested under three-point bending. Digital image correlation and computed tomography have been used to measure the full field displacement and internal defects, respectively. Furthermore, the theory of critical distances was applied to assess the mechanical strength of lattice structure specimens. The results have shown the strong influence of raster orientation on the mechanical strength and fracture patterns even for negative air gap values. The transition from brittle to ductile failure was observed when changing density and raster orientation. Lastly, neck-shaped defects were detected in knots of specimens manufactured with a grid pattern. Defects in grid pattern specimens appear due to the prescribed path followed by the extruder during the building process. They were the main source causing a decrease in the mechanical strength and fracture trajectories. The objective of this research is to enhance the knowledge on the mechanical response of 3D printed components and to give an in-depth failure assessment. [ABSTRACT FROM AUTHOR]

• Error quantification of the phase-field model in Westergaard's problem. • Assessment of different pre-crack definition approaches. • Verification of strain energy splits using an exact solution as a benchmark problem. • Application to mode I and mixed-mode loading conditions. One challenge in verifying strain energy splits in phase field fracture models is the lack of reference problems with exact solutions in mixed-mode loading that could serve as benchmark problems. In this work, different strain energy splits used in the variational phase field model have been applied to the classical Westergaard's problem. In contrast to other benchmark problems used in the literature, the proposed problem not only includes the singular term as a boundary condition but also implicitly considers all terms. To the authors' knowledge, this is the first time in the literature that this reference problem has been used to rigorously verify the accuracy of different energy splits of the phase field model. Several critical factors such as the pre-crack definition, mesh size, mixed mode ratio and the length scale parameter have been analysed. A good correlation between the numerical estimations and the analytical predictions was found for some pre-crack definition approaches under mode I. However, we demonstrated that the compatible regularisation length scale and mesh size are significantly lower under mode II loading (i.e., when the crack kinks) than under mode I. [ABSTRACT FROM AUTHOR]