Impact of Element Layout and Notching Technique on the Fracture Toughness of FFF-Processed Thermoplastics A. E. Patterson1,2,3,∗, C. Chadha4, I. M. Jasiuk4, J. T. Allison3 1 Faculty of Manufacturing and Mechanical Engineering Technology, Department of Engineering Technology and Industrial Engineering, Texas A&M University, College Station, TX, USA 2 Department of Mechanical Engineering, Texas A&M University, College Station, TX, USA 3 Department of Industrial and Enterprise Systems Engineering, University of Illinois at UrbanaChampaign, Urbana, IL, USA 4 Department of Mechanical Sciences and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA ∗ aepatterson5@tamu.edu Keywords: Additive manufacturing, fracture mechanics, experimental mechanics The mechanical performance of additively manufactured (AM) thermoplastic materials and polymer matrix composites is of great interest to designers considering the use of AM processes for manufacturing. While the basic mechanical properties for AM-created parts are well-studied in the literature, the fracture behavior is still an area in need of exploration. The fused filament fabrication (FFF) process is the most common and widely-used AM process for thermoplastic materials and polymer matrix composites. It is a scanning-type AM process which deposits and fuses discrete elements of material to form the part layers. Therefore, the layout pattern of the elements can be expected to greatly affect the fracture toughness of the materials as it affects the available crack paths in the material. In addition, the part shell (layer outline) will have an effect the fracture whenever a crack begins at or reaches a layer boundary as seen with printed notches; this consideration is an important driver for selecting part geometry and notching method. This study explored the effect of notching method and element layout pattern on the calculated fracture toughness for three common FFF materials: Acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), and polycarbonate (PC). To study the effect of notching, both printed and machined notches were used with and without pre-cracking (four different combinations) with ASTM D5045 CT samples (W = 30 mm, B = 6 mm). Three replications were completed (n = 12), with the collected data showing a statistically significant difference between the methods. Once completed and the best notching method selected, a set of similar samples (n = 72) with different element layouts (45-degree raster, gyroid, concentric) and element/bead thicknesses were tested. The results showed a very strong effect, with the fracture toughness ranging as much as 60% depending only on the element size and layout. The conclusions from this study were that both the notching method and the selection of element layout and size had a definite effect on the fracture behavior of three common FFF-processed materials and should be carefully considered when designing parts that will be fabricated using FFF. 63
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