Compression testing of pultruded carbon fibre-epoxy cylindrical rods

The fibre waviness inherent in conventional prepreg laminates significantly reduces their compressive strength. This waviness can be reduced through the use of unidirectional fibre rods. In this work, the development of a new test procedure and specimen design is reported that was used to determine the compressive properties of pultruded T300/828 and IM7/828 carbon fibre-epoxy unidirectional rods at room temperature. The IM7/828 system demonstrates a higher compressive strength than the T300/828 composite due to stronger fibres used and fewer manufacturing defects. Since the fibres as in tension primarily carry the compressive load, the final fracture of the rods occurs when the fibres fail. Post-failure examination reveals that failure of the fibres is microbuckling-induced. This is a bending failure as a consequence of buckling. Other events such as fibre-matrix debonding (splitting) and matrix yielding do not by themselves cause the final failure, but they facilitate fibre buckling by reducing the lateral support for the fibres. Microbuckling failure models are used to predict the compressive strength of the carbon fibre rods; agreement between theory and experiment is acceptable.