Tensile Behavior of Monazite Coated Nextel™ 720 Fibers and Tows

Abstract

The tensile strengths of Nextel™ 720 fibers, both bare and coated with monazite, and tows made of these fibers, were measured to study the effects of coating and thermal exposure. Close agreement was observed between the Weibull modulus obtained from the statistical fracture distribution and the modulus obtained from a study of the gage length dependence of strength. Thermal soaking for 24h at 1000, 1100 and 1200°C revealed significant differences in the behavior of coated and uncoated fibers. Uncoated fibers subjected to soaking for 24h at 1200°C retained 91% of their unsoaked strength, while similarly soaked coated fibers retained only 61%. The effect of coating reversed in the case of tows, with the presence of coating enabling higher strength retention after thermal exposure.