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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These results elucidate the experimentally observed decorrelation between strut density and Young's modulus, as documented in Table 2. Specifically, despite exhibiting a lower density (0.9451 g/cm³) compared to the 0.65 mm struts (1.1113 g/cm³), the 0.9 mm-wide struts demonstrate a higher Young's modulus (1648 MPa vs. 1307 MPa). This finding, consistent with observations reported by Sabé (2021) and Salem (2024) for ABS struts of varying section dimensions printed with parallel filaments, occurred despite all specimens being produced under controlled conditions and featuring good structural integrity, consistent densities within section sizes, and consistent Young's moduli within section sizes. The counterintuitive result is therefore proposed to arise from the fundamental dependence of stiffness on the spatial distribution of porosity and bonding regions, not nominal density alone; effective properties are governed by the real load-bearing area shaped by internal architecture.

Table 2: Measured d ensity and Young’s modulus of FFF-printed struts with varying nominal sections

Standard deviation [MPa]

FFF printed strut width [mm] (nominal CAD correspondence)

Mean Young's modulus [MPa]

Nominal strut section [mm 2 ]

Mean density [g/cm³]

0.6 x 4 mm 2 0.65 mm (60% CAD) 0.8 x 4 mm 2 0.9 mm (80% CAD) 1 x 4 mm 2 1.12 mm (100% CAD)

1.111 0.945 1.111

1307 1648 1930

53 30 21

3. Conclusions and open challenges This work deals with the prediction of the elastic behavior of single parallel FFF struts under uniaxial tensile loading. The developed numerical homogenization model integrates the heterogeneity effects of porosity and inter filament bonding mor phology within the strut’s microstructure. ABAQUS simulations, along with Voigt upper bound, demonstrate that variations in horizontal (in-layer) and vertical (interlayer) bonding moduli strongly impact the effective Young’s modulus. Overall, this approach provides a rigorous, microstructure-informed framework for accurately predicting the elastic response of FFF struts under uniaxial tension, supporting the optimization of interface quality to enhance mechanical performance. A key finding demonstrates that strut-level porosity exhibits a size dependent effect under some specific conditions. Additionally, an open challenge remains in fully understanding and accurately modeling the influence of porosity and bonding regions on Poisson’s ratio, which is critic al for capturing the complete elastic response of FFF struts. This challenge extends to predicting the behavior of lattice structures, where mechanical performance fundamentally depends on whether the architecture is tension-dominated (governed by axial strut forces) or bending-dominated (controlled by strut flexural rigidity). As established in seminal literature (Gibson & Ashby, 1997), bending-dominated lattices exhibit markedly lower stiffness and strength scaling laws compared to tension-dominated designs, making them highly sensitive to microstructural defects. The FEA framework will therefore enable critical investigation of how FFF-induced strut microstructure (including porosity gradients and interfacial bonding quality) influences flexural properties, particularly in bending-dominated regimes where local imperfections disproportionately compromise performance. Addressing this gap will be essential for developing comprehensive predictive models and optimizing the mechanical performance of additively manufactured components. Acknowledgements This study has benefited from the funding contributions of Region Normandy, France, through the TACTICS project 2023-2024 (RIN émergent) and of the Labex EMC3, CNRS, through the ATEMBILS project 2024. References Brenken, B., Barocio, E., Favaloro, A., Kunc, V., Pipes, R.B., 2018. Fused filament fabrication of fiber-reinforced polymers: A review. Additive Manufacturing, 21, 1 – 16.