Effect of Cleaning and Abrasion-Induced Damage on the Weibull Strength Distribution of Sapphire Fiber

Fractographic analysis revealed the presence of concurrent flaw populations in sapphire fibers which were tensile tested in the as-received condition (sized and unsized) and after various cleaning procedures. The following flaw populations were identified: surface flaws attributed to handling and abrasion damage (type A), volume or internal flaws attributed to shrinkage voids which form during the manufacturing process (type B), localized fiber surface reaction flaws introduced during the flame-cleaning procedure (type C), and self-abrasion surface flaws intentionally introduced on unsized fibers (type D). The strength distribution associated with each flaw type was characterized using a censored data Weibull analysis for both the least-squares and maximum-likelihood estimation methods. The strength distribution for type C (flame-cleaning) flaws exhibited an approximately 20% degradation in strength compared to the distribution for type A flaws. The strength distribution for type D (self-abrasion) flaws exhibited an approximately 35% degradation in strength compared to the strength distribution for type A flaws. This result underscores the need for fiber sizings to prevent damage during shipping and handling. However, higher purity sizings and/or improved procedures for sizing removal are required to mitigate cleaning-induced fiber strength degradation during composite fabrication.