Microscale equivalent modeling and experimental validation of CCF/PLA using a 100-to-1 downscaling strategy

Multiscale simulation of Fused Deposition Modeling (FDM) of Continuous Carbon Fiber reinforced Polylactic Acid (CCF/PLA) is constrained by filament-level geometric complexity. A “100-to-1” downscaling strategy is developed in which a regular filament cluster is simplified through equal-area square surrogates, thereby preserving fiber volume fraction (V_f) while substantially reducing geometric and computational burden. A Representative Volume Element (RVE) was implemented in analysis software using a regular rectangular array, Periodic Boundary Conditions (PBCs), and C3D6 wedge elements to evaluate effective engineering constants for three configurations (fully filled, gapped, and gap-free) across V_f = 35%–95%. The axial modulus predictions agreed closely with the Tandon–Weng model, with deviations below 2%, and remained within the Hashin–Shtrikman admissible bounds. However, the transverse moduli were higher than the Tandon–Weng predictions, with deviations mainly ranging from approximately 9% to 24%, whereas the shear moduli showed weaker and component-dependent deviations. This tendency is attributable to corner-induced stress concentration in square inclusions, shared-node compatibility, and the kinematic constraints imposed by the regular array. Nevertheless, the results remained physically admissible and exhibited a conservative stiffness-estimation trend, especially in the transverse direction. Furthermore, tensile testing of a single-track specimen (measured V_f ≈ 34%) supported the engineering utility of the proposed approach for predicting ultimate load (error ≈10%). The stiffness deviation between experiment and simulation (initial deviation ≈22%) was quantitatively interpreted by introducing a system-compliance correction mechanism, which partly reduced the apparent discrepancy and clarified the contribution of testing-system compliance. Overall, the proposed strategy retains accuracy for axial load-bearing behavior while providing an efficient and scalable microscale modeling basis for subsequent path- and structure-level simulations of FDM-printed CCF/PLA.