Anisotropic Behaviour of Extruded Short Carbon Fibre Reinforced PEEK Under Static and Fatigue Loading

The influence of fibre orientation on an extruded short carbon fibre PEEK composite, reinforced with 30% weight fraction of short carbon fibres, was investigated. Specimens were obtained from extruded plates along directions transverse and parallel to the extrusion flow and different types of fibre spatial arrangements were observed. Prior to fatigue testing the elastic modulus of each specimen was measured and the specimens were grouped into homogeneous families, from low to high modulus. Each family exhibited distinct fatigue strength, associated with different progressive damage patterns and failure mechanisms. With increasing alignment of the fibres along the loading axis, a noticeable improvement of fatigue strength could be observed, whereas when the fibres were mostly perpendicular, fatigue properties were even lower than those of unreinforced PEEK. Overall, results suggest that extruded short carbon fibre PEEK products may exhibit a heterogeneous microstructure and a wide range of fatigue properties, making the definition of design allowables a critical task.