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This paper discusses a new model and experimental characterization for thermal responses of straight twisted polymer fiber (TPF) actuators in blocked torsion. The proposed model is derived from combining the fiber stiffness matrix with Shafer’s model of free torsion. The derived model predicts that the blocking torque increases as the initial twist increases. Although it is not widely recognized, the tension of a straight TPF decreases as the initial torsion increases, and this paper explains this fact. The proposed model predicts the decrease in tension by using Shafer’s kinematic model that considers the effect of radial thermal expansion. Experimental characterization and model verification are performed using nylon 6 (polyamide 6) fiber samples with ten different initial twists, ranging from weak to strong. The results indicate that as the initial twist increases, the torque increases and the tension decreases. The tension fluctuates with respect to time. The experimental results show that the shear modulus increases as the initial twist increases. The predictions of the proposed model are reasonably consistent with the experimental thermal responses of straight TPFs in blocked torsion when the constants obtained by experimental characterization are used.

The selective-area growth of GaN (SAG-GaN) films on nonpolar bulk GaN substrates with trench patterns was performed by metalorganic vapor phase epitaxy. We investigated the transformation of SAG-GaN facet structures by changing the direction of the trench patterns. Anisotropic SAG-GaN structures with the () facet on the (0001) plane sidewall, the () facet on the top surface, and the () facet on the () plane sidewall appeared for trench patterns along the a-axis. The width of () facets decreased whereas () facets expanded with increasing off angle of trench patterns from the a-axis. On the other hand, hexagonal facet structures with {} facets appeared for trench patterns along the c-axis. () facets on the top surface expanded with increasing off angle of trench patterns from the c-axis, similar to the results of using trench patterns along the a-axis. Basal-plane stacking faults were annihilated by using trench-patterned substrates. Low basal-plane stacking fault (BSF) density and faster coalescence were obtained for the off angle of trench patterns of around 6° from the c-axis.