Compressive strengths of single carbon fibres and composite strands

Micro-compression and recoil tests have been carried out on single filaments of pitch- and polyacrylonitrile-based carbon fibres. Axial compression and bending tests were also carried out on unidirectional composite strands containing these fibres and a reduced compressive strength was calculated by dividing the fracture load of the composite strand by the cross-sectional area of the fibres. The fracture surfaces produced by different test methods were compared and a correlation between the compressive strength values determined by these test methods was investigated. The fracture surfaces of the fibres and composite strands showed different features depending on the type of fibre and matrix resin. The compressive strength of the composite strands increased with increasing matrix modulus. The compressive strengths of the fibres determined by the recoil test and from the axial compression test on the composite strand with a stiff matrix resin were almost in proportion to the strength determined with the micro-compression test.