Impact of Element Layout and Notching Technique on the Fracture Toughness of FFF-Processed Thermoplastics

This work explores the effects of notching method and element layout on the fracture loading properties of thermoplastic materials processed using fused filament fabrication (FFF). Three common thermoplastic materials were used (acrylonitrile butadiene styrene, polylatide, and polycarbonate). Four different notching methods were used, with printed and machined notches and with and without pre-cracking on ASTM D5045 compact tension specimens (n = 36). It was concluded that the notching method has a statistically significant impact on the sample preparation and that pre-cracking is necessary in all cases. Using this information to prepare specimens, a designed experiment using four different element layout strategies and two different nozzle sizes was completed with a total of 72 tests. The layout pattern was shown to have a very strong effect on the maximum fracture load, with the nozzle size showing a smaller but still statistically significant impact. With the exception of one layout using polycarbonate with likely design-driven printing defects, the results were very consistent through several replications. The results of this study are useful for making design decisions with FFF-processed materials, for better understanding the impact of the process design, and for working toward standardized printing and testing methods for additive manufacturing.