Fundamental Study of Compressive Strength Development in PAN-Based Carbon Fibers

Abstract : Evolution of mechanical properties in the conversion of two precursor polymeric fibers to carbon fibers has been studied. The focus has been on properties in axial compression of polyacrylonitrile (PAN, a semi rigid polymer) - and polybenzobisthiazole (PBZT, a rigid rod polymer) - based carbon fibers. Mechanical properties of fibers at different extents of progression toward the graphite fiber structure reveal that the evolutions of tensile and compressive properties are not synchronized. Substantial enhancements in both tensile and compressive strengths of carbon fibers occur only with the development of the carbonized morphology with its characteristic basal planes as the fundamental structural units. In addition, the recoil from tension method has been analyzed vis-a-vis axial compressive strength of carbon fibers. Fracture surfaces of specimens from this experiment do not necessarily reveal failure in a simple compression mode and especially includes bending. Statistical analysis of the recoil method demonstrates that the fiber failure distribution can be expressed by either a logistic or a Weibull distribution.