Nonlinear Shear Constitutive Modeling and Inverse Identification in Composites Using Edge‐Effect‐Free Tubular Torsion Tests

ABSTRACT Continuous fiber‐reinforced polymer matrix composites demonstrate significant and unique nonlinear mechanical behavior under shear loading. The free‐edge effects of conventional specimens in shear response experiments of composites have been simulated, revealing the capability of thin‐walled tubular specimens to minimize free‐edge disturbances for accurate constitutive characterization under high strain. An inverse identification framework was developed integrating multi‐island genetic algorithm (MIGA) with finite element analysis (FEA) specifically designed for torsion‐based evaluation of unidirectional thin‐walled tubular specimens. This methodology establishes a quantitative relationship between experimental torque‐angle measurements and intrinsic material behavior through systematic inversion procedures, enabling precise determination of nonlinear shear stress–strain responses without free‐edge effect interference. Experimental validation was performed through quasi‐static torsion experiments on [0] 6 glass/epoxy tubular specimens, demonstrating remarkable consistency between model predictions and experimental results in both elastic and progressively nonlinear behaviors. The tubular specimen combined with the inverse model demonstrates the feasibility of characterizing materials under high shear strain in composites devoid of free‐edge stress.