The compressive strength (in the fibre direction) of high-modulus (HM) carbon fibre/epoxy composites remains a critical limitation for designing composite structures. In this study, four-point bending tests were conducted on eighteen HM fibre–epoxy pairs to determine the compressive strength and failure strain of unidirectional plies in thick laminates. Experimental results were compared with predictions from a plastic fibre micro-buckling criterion including structural effects. Unlike previous studies with intermediate modulus fibres, major discrepancies were observed, with the model systematically overestimating experimental values. To explain these differences, the competition between plastic fibre micro-buckling and intrinsic fibre failure was investigated. An alternative criterion incorporating premature fibre crushing was applied using available fibre compressive strength data. The analysis reveals that, for most HM systems, compressive failure is governed by the intrinsic compressive strength of the fibres rather than by matrix-controlled shear instability. These results demonstrate that to enhance the compressive performance of HM composites, increasing the intrinsic compressive strength of HM fibres emerges as the primary lever for achieving higher structural efficiency.
Mechin et al. (Wed,) studied this question.