Carbon fibre compressive strength and its dependence on structure and morphology

Abstract

The axial compressive strength of carbon fibres varies with the fibre tensile modulus and precursor material. While the development of tensile modulus and strength in carbon fibres has been the subject of numerous investigations, increasing attention is now being paid to the fibre and the composite compressive strength. In the present investigation, pitch- and PAN-based carbon fibres with wide-ranging moduli and compressive strengths were chosen for a study of fibre structure and morphology. A rayon-based carbon fibre was also included in this study. Structural parameters (L c, La(0), L a(90), orientation parameter Z, and the spacing between graphitic planes d(00, 2)) were determined from wide angle X-ray spectroscopy (WAXS). Fibre morphology was characterized using high-resolution scanning electron microscopy (HRSEM) of fractured fibre cross-sections. The mechanical properties of the fibres, including compressive strength, the structural parameters from WAXS, and the morphology determined from HRSEM are reported. The influence of structure and morphology on the fibre compressive strength is discussed. This study suggests that the width of the graphitic sheets, the crystallite size perpendicular to the fibre axis (L c and L a(0)), and crystal anisotropy play significant roles in accounting for the large differences in compressive strengths of various carbon fibres.