Experimental Investigation of the Longitudinal Compressive Strength of Carbon Fibres with a Direct Measurement System

Characterization of the mechanical properties of carbon fibres is crucial to the design of fibre reinforced composite materials. However, little has been done due to the complexity and inaccuracy of some of the necessary tests. In order to study the compressive properties of single fibres, a direct system for single carbon fibre compressive strength was set up based on previous studies; several kind of PAN-based carbon fibres were examined at specimen gauge lengths from 20 to 150 μm using this system. It was discovered that the experimental compressive strength was constant when the length of carbon was in the range of 20~90 um; when the sample's length was beyond 90 μm, the compressive strength decreased sharply. The reason is that its deformation mode was not compressive but buckling. In order to compare with corresponding tensile behaviour, a tensile strength test was also carried out, and it was discovered that the compressive strength was about 50% of the tensile strength for single fibres.