PSI - Issue 77

Sergio Cicero et al. / Procedia Structural Integrity 77 (2026) 56–63 Sergio Cicero et al./ Structural Integrity Procedia 00 (2026) 000 – 000

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2. Materials and methods The five materials analyzed in this work have been extensively studied in previous studies (Cicero et al. (2020), Cicero et al. (2021), Cicero et al. (2024), Cicero et al. (2025)), where the reader can find details of the different investigations. All of them share some common conditions: Fracture test specimens according to ASTM D6068 (2018), since they do not always meet linear elastic fracture conditions (typical of ASTM D5045 (2014)). In all cases, the specimens are three-point bending (SENB, Single Edge Notch Bending). • The fracture specimens are tested with U-shaped notches with radii ranging from 0 mm (cracks) to 2 mm. The notches were machined, not printed, to eliminate additional local anisotropies at the bottom of the defect. • The five materials were printed in three different raster orientations: 0/90, 45/-45, 30/-60. The printing conditions for each material were those established commercially by each filament manufacturer; therefore, they are not exactly the same for the five materials. Specifically, they were as follows: • ABS (Cicero et al. (2020)): layer height: 0.3 mm; line width: 0.4 mm; infill: 100%; printing temperature: 230°C; bed temperature: 95°C; printing speed: 40 mm/s. • PLA (Cicero et al. (2021)): layer height: 0.3 mm; line width: 0.4 mm; infill: 100%; printing temperature: 200°C; bed temperature: 75°C; printing speed: 30 mm/s. • ASA (Cicero et al. (2024)): layer height: 0.2 mm; line width: 0.42 mm; infill: 100%; print temperature: 250 °C; bed temperature: 90 °C; print speed: 40 mm/s. • PLA-Gr (Cicero et al. (2021)): layer height: 0.3 mm; line width: 0.4 mm; infill: 100%; printing temperature: 200°C; bed temperature: 75°C; printing speed: 30 mm/s. • ASA-CF (Cicero et al. (2025)): layer height: 0.2 mm; line width: 0.42 mm; infill: 100%; print temperature: 250 °C; bed temperature: 90 °C; print speed: 40 mm/s. The tensile specimens used, always with geometry according to standard, can be found in Cicero et al. (2020), Cicero et al. (2021), Cicero et al. (2024), and Cicero et al. (2025). The geometry of the fracture specimens is almost identical for the five materials, a schematic example being shown in Figure 1. The only difference is that the thickness of ASA and ASA-CF is 5 mm, compared to 4 mm for ABS, PLA and PLA-Gr. • Tensile test specimens according to ASTM D638 (2014). •

Fig. 1. Geometry of ABS and PLA specimens, for a given notch radius (ρ). Dimensions in mm.

The fracture resistance results are quantified in terms of apparent fracture toughness (K N cracked specimens coincides with the fracture toughness of the material (K mat ). Subsequently, the K N mat results are analyzed using the TDC, which comprises different methodologies, all characterized by the use of a material length parameter called the critical distance (L). In fracture analyses, L follows equation (1): = 1 ( ) 2 (1) where K mat is, again, the fracture toughness of the material and σ 0 is the inherent strength of the material. In materials with linear elastic behavior at both the micro and macro scales, σ 0 coincides with the material's tensile strength ( σ u ), while in materials with nonlinear behavior, as in the case of those studied in this work, σ 0 requires calibration. The methodologies comprising the TDC are based on knowledge of the stress field generated at the defect tip (Taylor (2007)). Two of them, the Point Method (PM) and the Line Method (LM), offer the best balance between the mat ), which in the case of