Surface damage and environmental effects on the strain-rate sensitivity of the strength of sapphire and silicon carbide filaments

Abstract

c-axis sapphire and silicon carbide-on-carbon filaments with pristine and damaged surfaces were tensile tested in water and dry toluene at various strain rates. There was no evidence of slow crack growth during the testing of the silicon carbide filaments. However, the surface damaged sapphire filaments exhibited slow crack growth in the water environment. The slope of the stress intensity factor versus crack velocity curve in region I of the characteristic curve was found to be 28 in excellent agreement with previous results from slow crack growth studies in which the stress corrosion phenomenon is adequately explained by the Hillig-Charles mechanism. The corresponding tests in dry toluene produced no evidence of slow crack growth. The sapphire filaments with virgin surfaces exhibited slow crack growth in both water and toluene which is apparently not related to the moisture assisted growth observed in the abraded filaments.