Static assessment of notched additively manufactured polymers based on the theory of critical distances

The aim of this paper is to review the work we have done in recent years to investigate the accuracy of the Theory of Critical Distances (TCD) in estimating static strength of notched additively manufactured acrylonitrile butadiene styrene (ABS) and polylactide (PLA). The TCD takes as its starting point the assumption that the extent of damage under static loading can be assessed successfully by using two different material parameters, i.e. (i) a critical distance whose length is closely related to the material micro/meso/macro-structural features and an inherent (i.e. a defect free) material strength. Plain and notched specimens of 3D-printed PLA and FDM were manufactured (with an in-fill level of 100%) by making the deposition angle vary in the range 0°–90°. Using the TCD, failures were predicted by directly postprocessing the linear-elastic stress fields determined by solving standard linear-elastic Finite Element (FE) models. Independently of notch sharpness and printing direction, the estimates being obtained were found to be highly accurate, falling within an error interval of about 20%. This result fully supports the idea that the TCD can successfully be used in situations of practical interest to design against static loading notched components of additively manufactured polymers by directly postprocessing the results from simple linear-elastic FE models.