At present, the concept of artificial muscle twisted by polymers or fibers has become a hot issue in the field of intelligent material research according to its distinguishing advantages, e.g., high energy density, large-stroke, non-hysteresis, and inexpensive. The axial thermal expansion coefficient is an important parameter which can affect its demanding applications. In this letter, a device with high accuracy capacitive sensor is constructed to measure the axial thermal expansion coefficient of the twisted carbon fibers and yarns of Kevlar, and a theoretical model based on the thermal elasticity and the geometrical features of the twisted structure are also presented to predict the axial expansion coefficient. It is found that the calculated results take good agreements with the experimental data. According to the present experiment and analyses, a method to control the axial thermal expansion coefficient of artificial muscle is proposed. Moreover, the mechanism of this kind of thermally driven artificial muscle is discussed.
Current transport in grain boundary is one of the crucial factors which can affect the macro-supercurrent characteristics of the high temperature superconductors. van der Laan et al. [Phys. Rev. Lett. 103, 027005 (2009)] presented the strain dependence of the critical current density with a power-law fitting function, which has been verified by many experimental measurements. Here, we present a theoretical analysis of current transport in the [001]-tilt low angle grain boundary according to the strain energy of dislocation. An analytical expression is obtained which has the similar form of the fitting function, and in which the physical characteristics of parameters are distinct, and their values are close to the reports in literature.
The conductors used in large fusion reactors, e.g. ITER, CFETR and DEMO, are made of cable-inconduit conductor (CICC) with large diameters up to about 50 mm. The superconducting and copper strands are cabled around a central spiral and then wrapped with stainless-steel tape of 0.1 mm thickness. The cable is then inserted into a jacket under tensile force that increases with the length of insertion. Because the cables are long and with a large diameter, the insertion force could reach values of about 40 kN. The large tensile force could lead to significant rotation forces. This may lead to an increase of the twist pitch, especially for the final one. Understanding the twist pitch variation is very important; in particular, the twist pitch of a cable inside a CICC strongly affects its properties, especially for Nb 3 Sn conductors. In this paper, a simplified numerical model was used to analyze the cable rotation, including material properties, cabling tension as well as wrap tension. Several rotation experiments with tensile force have been performed to verify the numerical results for CFETR CSMC cables. The results show that the numerical analysis is consistent with the experiments and provides the optimal cabling conditions for large superconducting cables.
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