Characteristics of compressive failure behavior of polyacrylonitrile‐based carbon fiber multifilament

The deformation characteristics exhibited by the hierarchical structure in composites and their influence on compressive properties are investigated by controlling the deformation of carbon fiber multifilament under axial compressive loading. Our findings reveal that the deformation curve of carbon fiber composite materials under axial compression loads is nonlinear. Specifically, for 12 K high‐strength and medium‐modulus carbon fiber multifilament, when the compression load exceeds approximately 600 N, the buckling of individual fibers leads to shear deformation that damages the interface between the fiber and resin. Consequently, the compressive deformation of the multifilament composites transitions from elastic to plastic deformation. By enhancing the support force exerted by the resin on the multifilament composite and reducing the load span within the range of 2–4 mm, it is possible to effectively minimize or eliminate the overall buckling that may occur during the compression process of the multifilament composite. This results in a higher secant modulus under the same level of deformation. Additionally, it reduces the step difference between the compression and tension regions in the cross‐section of carbon fiber formed by the buckling, while the compression strength of the carbon fiber multifilament increases from 2.32 to 4.78 GPa. Highlights Characteristics of compression deformation of carbon fiber multifilament. Regulation of the degree of buckling of carbon fiber multifilament. Cross‐section morphology under different compression failure mechanisms. Influence of the degree of buckling on compressive properties of carbon fiber. By enhancing the support force exerted by the resin on the multifilament composite and reducing the load span within the range of 2–4 mm, it is possible to effectively minimize or eliminate overall buckling that may occur during the compression process of the multifilament composite. This results in a higher secant modulus under the same level of deformation. Additionally, it reduces the step difference between the compression and tension regions in the cross‐section of carbon fiber formed by the buckling, while the compression strength of the carbon fiber multifilament increases from 2.32 to 4.78 GPa.