Reliability Of Hard Plastic Clad Silica Fibers

By CeramOptec Industries Inc.

The numerical apertures for the different fibers in this study were made using a set up which involved taking diameter measurements of the projections onto a black surface shielded from direct ambient light at five different distances from the fiber end. A white light source was over-launched and overfilled into the input end of the fiber. Meter long samples were used with about a 180 degree angle bend relative to the output end. The bend radius was on the order of a 40-50 cm. The ends were secured to metal blocks to guarantee stability of placement during testing and to improve reproducibility. NAs calculated at the five distances were averaged to yield the reported NA.

The primary mechanical property reported is the dynamic strength as measured by a universal testing machine and plotted on a Weibull plot. Gauge length was 1 meter. The fiber is stretched while horizontal and anchored at the two ends by wrapping several loops around a tapped mandrel of approximately 10 cm diameter. About 1.7 meters of fiber is consumed per trial. Results presented below are generally from one or two fibers where 15-20 samples are taken from a specific fiber run. Tests were made at ambient temperature and relative humidity. Temperatures ranged in the 20-27 C, and relative humidity [RH] primarily was 30% 7%, although some samples were tested with RH at 72%. Strength data are plotted according to the generally accepted Weibull approach.

Additionally the static fatigue behavior has been measured also. Tests use half meter gauge lengths with the fiber wrapped snuggly around a metal rod, anchored at the ends with waterproof tape. The wrapped samples are then immersed in room temperature water and the time to failure is recorded. Typically at least five fiber samples are measured for each rod diameter, i.e. bending stress level. Affects of fiber jacket thickness are incorporated into the stress calculations. The data are plotted based on the power law, which is still the most generally accepted approach to presenting static fatigue data.