Methodology for testing the compressive strength of pultruded composites

Unidirectional (UD) composites with 0° fibre orientation have high axial strength along the direction of fibres. Hence, the axial compressive testing of 0° UD composites is extremely difficult due to associated issues like misalignment, buckling, non-uniform gripping and non-uniform stress distribution. These issues can intensify during fatigue testing, especially at higher load levels. The data available in the literature on the compressive response of unidirectional fibre reinforced composites is scarce. Many researchers have attempted designing a standard testing fixture for compressive testing of the fibre reinforced polymers (FRPs). Two most common fixtures are Boeing-modified ASTM D695 end loading fixture and ASTM D6641 combined loading compression (CLC) fixture. However, these fixtures are only feasible for compressive testing of the rectangular composite laminates. There is no standard fixture for compressive testing of cylindrical pultruded composites. This paper presents a methodology for testing the compressive strength of pultruded cylindrical composites. A fixture is designed and fabricated to conduct the tests. Different misalignment, gripping and stress concentration issues that could occur during the compression testing are addressed and a corresponding solution is provided. Unidirectional (UD) carbon/epoxy pultruded rods are used as test specimens. The test data of 21 specimens is presented and the failure modes are analysed using scanning electron microscope (SEM) images.