Micromechanical Prediction of Young’s Modulus in Electrospun Nanofiber-Reinforced Polymers: Model Applicability and Data-Reporting Limits

Classical micromechanical models are widely used to estimate composite stiffness, but their transferability to electrospun-fiber-reinforced polymers is uncertain because the reinforcement forms a continuous, often random, network whose effective properties depend on fiber diameter, orientation, architecture, and processing. This study uses six diagnostic case studies from three published composite studies with polyamide 6 (PA6) fibers in poly(ε-caprolactone) (PCL), poly(methyl methacrylate) (PMMA), and poly(lactic acid) (PLA) matrices to test whether the rule of mixtures, Halpin–Tsai, and Tsai–Pagano relations remain predictive when the fiber modulus must be taken from an independent single-fiber study, as is often unavoidable when utilizing data from the literature. With a PA6 single-fiber modulus of 901.65 MPa, all relations fall below the measured moduli. The Reuss–Voigt spread is at most 64 MPa, whereas prediction–experiment differences reach about 4.2 GPa. Uncertainty propagation and sensitivity to density, Halpin–Tsai shape parameter, orientation efficiency, and fiber-modulus choice classify one PLA/PA6 composite as a robust bound violation (required apparent fiber modulus ≥ 166 GPa), a second as a nominal violation, the PCL/PA6 series as input-ambiguous, and the PMMA/PA6 case as inconclusive. The choice of the model is therefore a smaller source of error than the definition of the input phases. A minimum reporting framework is proposed for future micromechanical and data-driven prediction.