A Refined Analytical Model Incorporating Fiber Length, Orientation, and Loading‐Angle Effects for Predicting the Young's Modulus of Short Fiber Composites

ABSTRACT Predicting the modulus of short fiber‐reinforced composites is complicated by simultaneous variations in fiber length, orientation, and volume fraction during processing. This work refines the classical modified rule of mixtures (MROM) by introducing two concentration‐dependent weighting functions, and , which capture the evolution of effective fiber length, fiber‐fiber interactions, fiber orientation, and loading‐angle effects. A microstructural efficiency coefficient is further incorporated to describe reinforcement degradation from dilute to crowded fiber conditions. The model was validated using ethylene‐vinyl acetate/short carbon fiber composites with fiber volume fractions of 1.37%–16.80%. Young's modulus measured at loading angles of 0°, 45°, and 90° showed excellent agreement with predictions, with the refined formulation outperforming the classical MROM, particularly at higher loading angles. Overall, the refined framework provides a compact and physically grounded framework for accurately predicting stiffness and supports the design and optimization of short fiber‐reinforced polymer systems.