Crack resistance, strength and dynamic fatigue of quartz fibers with copper coatings

Abstract

Metallized coatings can significantly improve the operational properties of quartz fibers. The research was conducted to determine the crack resistance, strength and dynamic fatigue of optical fibers without any coating and with copper coatings. The microhardness of quartz fibers was measured by the diamond indentation of end surfaces. The stress intensity parameter K1cwas found from the A. Niihara semi-empirical dependence. The geometry of indentation and radial cracks was studied using a scanning electron microscope. The crack resistance of uncoated quartz turned out to be almost 3 times less as compared to the copper coating fiber, which is presumably due to the additive contribution of compressive stresses on fiber surfaces and quartz wetting with copper. Copper-coated optical fiber drawing increases the tensile strength, crack resistance and dynamic fatigue parameter, and it is the main resource for maintaining operation in the conditions of a statistical approach to structural strength. Comparative tests were conducted to check the optical fiber strength by two-point bending and axial tension methods. Experimental tests conducted to check the ultimate mechanical strength of quartz optical fibers showed a significant spread of data, which indicates the presence of cracks of various sizes in a brittle solid and is a characteristic feature of brittle fracture as suggested by the A. Griffiths theory. In addition, it was assumed that the chaotic distribution of defects and microcracks extends along the entire length of a brittle solid, a quartz optical fiber in this case. A statistical model based on the Weibull distribution was used to describe surface microcracks depending on the fiber length. As a result, Weibull graphs were plotted in coordinates connecting the probability of failure with the strength, fiber length and parameter describing the ultimate strength.