The Effect of Microcrystals on ZrF4–BaF2–LaF3–AlF3–NaF Glass Fiber Fracture

The mechanical response of materials to an applied force is determined by the inherent microstructure properties of the material.Microcrystals formed during heating and fiber drawing represent inherent flaws, which play a strong role in the mechanical properties as well as the handling ability of optical waveguides, in particular ZBLAN (ZrF4–BaF2–LaF3–AlF3–NaF) fibers. The property of the fiber to flex and bend is useful for handling and positioning the fiber in a desired application. A series of ZBLAN fibers were bent to specific radii of curvature to determine the applied curvature at which fiber fracture occurs. The fibers were first subjected to a tailored temperature arrangement for a designated amount of time to induce varying amounts of crystal formation. The fiber failure was documented and photographed with the aid of optical microscopy and scanning electron microscopy. Fracture mechanics analysis was used to characterize the impact of crystal size on the failure of the ZBLAN fiber. The results of this assessment show the impact of thermal degradation on ZBLAN fibers as well as suggest an optimum fiber drawing take-up reel diameter.