Bend properties of sapphire fibers at elevated temperatures I: Bend survivability

The effect of temperature on the bend radius that a c-axis-oriented sapphire fiber can withstand was determined for fibers of various diameter. Bend stress rupture tests were performed for times of 1–100 h and temperatures of 300–1700 °C. Fibers would survive the bend test undeformed, would fracture or would deform. The bend survival radius was determined to be the radius above which no fibers fractured or deformed for a given time-temperature treatment. It was found that the ability of fibers to withstand curvature decreases substantially with time and increasing temperature and that fibers of smaller diameter (40–83 μm) withstood smaller bend radii than would be expected from just a difference in fiber diameter when compared with the bend results of the fibers of large diameter (144 μm). This was probably due to different flaw populations, causing high temperature bend failure for the tested sapphire fibers of different diameters.