The Effect of Pores on Compressive Failure of Highly Aligned Carbon Fibre Reinforced Epoxy Composite Rods Produced by Pultrusion

Compressive strengths have been measured for two grades of pultruded epoxy 67vol% carbon fibre composite. Differences in the pultrusion conditions for the two grades led to relatively high porosity levels in the interior of one of them, while the other was effectively pore-free. Both exhibited excellent fibre alignment. Despite this, initial measured strengths were relatively low (~1.7-1.8 GPa), with little difference between the values obtained for the two grades. This is explained, with the help of FEM modeling work, as being due to the generation of stress concentrations near the end of the gauge length at the specimen periphery, where the two grades exhibited similar (pore-free) microstructures. Further measurements indicated that the true strengths were about 2.7-2.8 GPa for the pore-free material and about 2.1 GPa for the porous material. These values are broadly consistent with the expected effect of the presence of the pores, which tend to promote shearing parallel to the fibre axis, leading to formation of kink bands and consequent failure.

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