PSI - Issue 80

R. Salem et al. / Procedia Structural Integrity 80 (2026) 256–268 Rania Salem/ Structural Integrity Procedia 00 (2019) 000 – 000

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The mechanical behavior of the material is governed primarily by (i) the porosity, which decreases load bearing capacity and initiates stress concentrations, and (ii) the bonding regions, which influence the mechanical connectivity between adjacent filaments and affect stiffness and strength anisotropy. The evolution of porosity as a function of the filament radius-to-spacing ratio (r/b) defines five distinct microstructural regimes, labeled Zones I to V in Fig. 3 : ▪ Zone I: No bonding regions are present. The structure consists only of reference FFF material and voids, resulting in high porosity. ▪ Zone II: The first bonding regions begin to form when the filament radius r reaches half the horizontal spacing between filaments ( r=b ). Porosity starts to decrease. ▪ Zone III: All bonding regions are present, yet voids remain. The structure includes both FFF reference material and porosity, with continued reduction in porosity fraction. ▪ Zone IV: This marks the limit for the generation of four bonding regions, beyond which the voids are nearly eliminated, and the bonding network is fully developed. ▪ Zone V: No porosity remains. The structure is composed solely of FFF reference material and fully developed bonding regions, including vertical bonding. This modeling framework is valid within Zone III, where all four distinct microstructural phases can be individually identified. Beyond this zone (i.e., in Zone V), the microstructure no longer contains voids, and the RVE ceases to represent the heterogeneous phase distribution accurately.

Fig. 3.: Generation of bonding regions

2.1.2. Material phase assignment

To accurately capture the anisotropic mechanical behavior observed in the FFF of ABS, the RVE model differentiates between the horizontal bonding region (HBR), vertical bonding region (VBR), solid filament domains or non-bonded regions (NBR), and voids (p). This classification reflects the distinct thermal histories and cooling rates experienced during layer-by-layer deposition, which influence polymer chain mobility, interdiffusion, and interfacial