Compressive testing of thermoset composites reinforced with high-performance polymer fibres

High-performance polymer fibres offer promising tensile and physical properties but are rarely used in structural composite applications due to their poor compressive performance. To better understand their performance inside a composite, unidirectional thermoset composites made with three types of polymer fibres were tested in shear-loaded compression. The results confirmed the poor compressive performance of the composites despite good fibre alignment, low porosity, and decent interfacial adhesion. Showing that the fibres collapse rather than microbuckle proves that intrinsic fibre behaviour in compression is the key culprit. The developed finite element model predicted that the short gauge lengths required to avoid buckling lead to significant strain concentrations due to the grips. This causes the test to underestimate the compressive modulus and potentially the rest of the compressive stress in the stress-strain diagram.

Automated summary

High-performance polymer fibres have excellent tensile and physical properties but poor compressive performance, which limits their use in structural composite applications. Testing unidirectional thermoset composites made with three types of polymer fibres in shear-loaded compression confirmed their poor compressive performance despite good fibre alignment, low porosity, and decent interfacial adhesion. The collapse of the fibres rather than microbuckling was identified as the main cause. The finite element model developed predicted that the short gauge lengths needed to avoid buckling led to significant strain concentrations due to the grips, resulting in underestimation of the compressive modulus and potentially the rest of the compressive stress in the stress-strain diagram.