Fracture mechanisms in carbon fibres derived from pan in the temperature range 1000-2800 degrees C

Abstract

Structural parameters derived from absolute intensity small-angle X-ray scattering experiments have been combined with strength and failure strain data for pan carbon fibres in an elastic/plastic theory of fracture. Good quantitative agreement with the theory is obtained throughout the heat treatment temperature range of 1000-2800 degrees C. The application of a modified griffiths theory, including a plastic work term, gives more qualitative agreement. The influence of the microstructure, in the form of crystalline ribbons, elongated micropores, and non-organized carbon and nitrogen, is discussed in relation to the fibre failure strain. The influence of grosser internal flaws on mechanical properties is also considered.