Standardized twisted polymer actuators: Quantitative modeling and morphing wing validation

Twisted-and-coiled polymer actuators (TCPAs) based on spandex offer large stroke and low-cost fabrication; yet, their reproducible design and operational stability remain constrained by ad-hoc processing and incomplete electro-thermo-mechanical descriptions. This work develops an integrated fabrication-to-function framework that quantitatively connects process parameters, helical geometries, and actuation responses, validated using single-fibre tests, to an application-level demonstrator. Systematic experiments delineate how the pre-stretch ratio, twist density, and winding load shape the helix formation and free-stroke strain, leading to a reproducible fabrication criterion that eliminates empirical trial-and-error. A compact analytical model that couples anisotropic thermal expansion with helical kinematics is calibrated under free-stroke conditions, accurately predicting strain-time trajectories across power densities (Coefficient of determination = 0.953; root mean square error = 1.16%). Mapping the power-response landscape further identifies a stability window (stable at 23.4 mW·mm^-1; degraded beyond 25.2 mW·mm^-1) and clarifies the mechanisms of failure, including modulus softening, helix-angle drift, and friction-induced losses. Scaling by parallel fibre bundles enhances the load capacity (∼3 N for a 16-fibre TCPA) without compromising the strain output. Finally, a differentially driven morphing wing demonstrates continuous and controllable bending between 0° and 26.7° (≈15° within 10 s at 23.4 mW·mm^-1), confirming system-level practicality. By uniting a reproducible fabrication rule, calibrated geometry–anisotropy model, and mapped power-density regime, this study transforms TCPA development from intuition-based tuning to prediction-guided engineering, advancing their applications in adaptive structures and soft robotics.