Damage and failure of SiC fiber tows during environment activated slow crack growth: Residual behavior and Strength-Probability-Time diagrams

Abstract

The paper investigates the damage and failure of fiber tows induced by slow crack growth activated by environment and applied load. The investigation is based on calculation of residual strengths and stress-lifetimes using models of slow crack growth on filaments and residual tensile behavior of fiber tows. This approach allows an exploration of behaviors and phenomena that cannot be assessed experimentally owing to various practical difficulties related to temperature and variability. It was applied to SiC-based Hi-Nicalon and Hi-Nicalon S fibers. Effects of constant deformation or force loading modes at high temperature in air were examined. Damage and rupture of fiber tows were described using the statistical distributions of filament residual strengths and lifetimes, tow residual behavior and Strength-Probability-Time (SPT) diagrams for critical filaments. The predicted SPT diagrams were compared to available experimental results obtained on tows and 2D woven SiC/SiC. Introduction of the effects of failure of groups of filaments in the model shed light on the trends in experimental results. The analysis highlighted the superior resistance to slow crack growth of Hi Nicalon S over Hi Nicalon which was related to superior fast fracture strength and toughness.