Analysis of flaws in high-strength carbon fibres from mesophase pitch

Abstract

Defects in mesophase pitch-based carbon fibres were studied by using scanning electron microscopy and energy dispersive X-ray analysis. A novel fractography technique permitted routine recovery of the primary fracture surfaces of filaments tested in tension. The carbon fibres included experimental monofilaments spun on laboratory equipment and multifilaments spun as a continuous fibre on production-type equipment. Carbon monofilaments and multifilaments from clean mesophase pitches were stronger than similarly prepared fibres from contaminated pitches. Reduction in the levels of contamination allowed fibres to be processed at high heat-treatment temperatures without sacrificing tensile strength. Results from a Weibull analysis of the tensile strength of clean multifilaments as a function of test gauge length were consistent with microscopy observations that strength-limiting surface flaws were closely spaced along the filaments.