Abstract
An apparatus measuring the compressive behavior of single fibers in the transverse direction conveniently with sufficient accuracy was developed. In this apparatus, a single fiber was compressed between two glass plates, and the compressive displacement of the fiber was determined by applying the optical interference occurring between the two glass plates. By using this apparatus, the compressive behavior of a series of PAN-based and pitch-based carbon fibers were investigated, and the following features were ascertained : 1) carbon fibers can be deformed reversibly by the transverse compression up to a displacement corresponding to about 10% of diameter ; 2) as the fiber is compressed in the transverse direction, the compressive deformation becomes more difficult for PAN-based carbon fibers, while for pitch-based carbon fibers, the compressive deformation becomes easier; 3) the transverse modulus tends to decrease with increasing crystallite orientation to the fiber axis direction. The experimentally observed relationship between the transverse modulus and the crystallite orientation can not be explained by the fiber structure models assuming that uniform stress or uniform strain is applied to the crystallites randomly distributed in a fiber cross-section. This suggests that the transverse modulus changes dependently on the fiber texture composed of crystallite aggregates. The transverse compressive strength of pitch-based carbon fibers decreased with increasing crystallite orientation. The SEM photographs of the fractured fibers are shown.
