Small-Strain Tensile Characterization and Finite Element Calibration of Sodium Alginate-Based Biomimetic Artificial Muscle Strips

Abstract This study investigates the small-strain tensile response and finite element calibration of sodium alginate-based biomimetic artificial muscle strips and extends the calibrated mechanics to an electro-ionic-mechanical model. The Ni-doped formulation was selected from our previous optimization of actuation and electrochemical performance. Quasi-static uniaxial tensile tests were performed on three undoped and three Ni-doped specimens. Equivalent moduli were extracted over 0–5% engineering strain, where both groups showed approximately linear responses. The undoped and Ni-doped groups exhibited moduli of 0.975 ± 0.212 MPa and 1.118 ± 0.474 MPa. With n = 3 per group, the between-group comparison was inconclusive (Welch’s t test, p ≈ 0.67) and should not be interpreted as evidence of equivalence. A two-dimensional plane-stress model was calibrated against the group-level tensile responses. The model reproduced the initial stiffness and showed stress concentration near the fixed end and interlayer transition regions. The calibrated mechanical framework was extended under 3 V excitation by coupling electrostatics, ion transport, differential swelling, and solid mechanics. The multiphysics model reproduced the overall 0–1000 s output-force evolution with an RMSE of 0.0992 mN, an MAE of 0.0757 mN, R2 = 0.8152, and a plateau-force error of 3.76%. These results provide experimentally based mechanical parameters and a computational framework for subsequent voltage-dependent studies.