Frictional Behavior of a Micro-sized Superconducting Fiber in a Low-Temperature Medium: Experimental and Computational Analysis

Abstract

The purpose of the current study is to explore the frictional behavior of a micro-sized superconducting fiber at the low-temperature condition. At first, a highly precise tribometer composed of a superconducting fiber wrapping around a cylinder made of pure Cu was immersed in liquid nitrogen. The force and displacement resolutions of the experimental system were as high as $$0.01\, \hbox {mN}$$ and $$0.03\,\upmu \hbox {m}$$ , respectively. The NbTi fibers with diameters ranging from 22.9 to $$115\,\upmu \hbox {m}$$ were used in the experiments, and their frictional behaviors in three media, i.e., liquid nitrogen, air and water, were systemically investigated. It was found that the frictional force in air showed a remarkable size effect. The existence of water medium could significantly reduce the frictional force, but could not eliminate the size effect. For the samples with the same diameter, the frictional force in liquid nitrogen was about 1.4 times of that in air, accompanied with remarkable stick-slip phenomenon. Notably, the fiber’s frictional behavior in liquid nitrogen showed no dependence on diameter. In order to interpret these phenomena, the frictional behaviors of the fibers in air, water and liquid nitrogen were simulated using a modified spring-slider model, by taking into account the influence of hydrophilicity on surface roughness, and the influence of surface roughness on the fiber’s frictional behavior. The simulation results were consistent with the experimental data qualitatively.