Fig. 2. Mechanical characterization of fiber-based artificial muscle.
(A) Stress-strain curves recorded at different extension rates for precursor fibers (without PMMA cladding) with a cross-sectional area of 300×470 μm2. (B) Change in the spring diameter with respect to the deformation rate. (C) Spring diameter and number of coils versus applied pre-strain. Error bars and shaded areas represent average and standard deviation, respectively. The number of samples n=5. (D) Change in the spring index with respect to spring diameter and actuation strain. (E) Change in the actuation stress-strain (grey) and work capacity (green). Attributes of the fibers are k=6, 6 turns/cm (continuous line); k=5, 10 turns/cm (dashed line); k=5.5, 12 turns/cm (dot line). (F) Change in the residual stress with respect to the cross-sectional area. (G) The setup used for the force measurement of the fibers with 300×470 μm2 cross-section (scale bar is 5 mm). For the fibers with a 8×12.5 μm2 cross-section (scale bar is 200 μm), a similar setup was used. The optical heat source was replaced with a micro-Peltier heater and a force gauge had a higher resolution. (H) Temperature and force responses to photothermal pulses collected for a fiber with 300×470 μm2 cross-section (k=5, 8 turns/cm). (I) Generated force vs. the temperature difference (number of cycles 300) for fibers with 200×312 μm2 cross-section (k=5, 10 turns/m). Navy blue, cerrulean blue, cyan, and green data point clusters represent different temperature ranges of 3.32±0.26 °C, 5.28±0.37 °C, 9.74±0.34 °C, and 12.98±0.74 °C, respectively. (J) Temperature and force responses to thermal pulses for a fiber with an 8×12.5 μm2 cross-section (k=4.6, 60 turns/cm). (K) Change in the efficiency with respect to actuation strain (blue line k=6, 6 turns/cm; green line k=5, 10 turns/cm; grey line k=5.5, 12 turns/cm). (L) Force measured across 300 thermal actuation cycles applied over 3 consecutive days for a fiber with 200×312 μm2 cross section (k= 5, 10 turns/cm). Inset: A single actuation cycle.