Elastic bending radius calculation of metallic attenuated total reflection GeO₂ hollow optical fibers

A metallic attenuated total reflection GeO₂ hollow optical fiber can be very robust for transmitting a CO₂ laser beam because of high toughness and high thermal dissipation ability of the metal tube. However, the plastic deformation behavior of a metal may cause irreversible (plastic) deformations as the metallic hollow optical fiber is used to deliver a laser beam. To avoid this, it is necessary to obtain the elastic bending radius of a metallic hollow fiber and maintain the fiber under an elastic bending condition in practical applications. This work aims to study the elastic bending radius of a metallic GeO₂ hollow fiber. The elastic bending radii are calculated based on the elastic-plastic bending theory of a metal pipe and the fabrication process parameters of stainless steel or beryllium copper GeO₂ hollow fibers. Then, the calculated radii were experimentally investigated. The stainless steel hollow fiber (internal diameter is 1.4 mm, wall thickness is 0.025 mm) exhibits elastic bending behavior when the yield strain is below 0.29%, and the minimum elastic bending radius reaches 249.61 mm. The beryllium copper hollow fiber (internal diameter is 1.4 mm, and wall thickness is 0.05 mm) is elastically bendable as the yield strain is lower than 0.375%, and the minimum elastic bending radius is 199.58 mm. The calculated minimal elastic bending radii agree with the measured values of the stainless steel or beryllium copper hollow optical fibers.