Investigation on three-dimensional defect evolution and damage mechanisms of continuous carbon fiber reinforced PEEK composites under tensile loading

Continuous carbon fiber-reinforced polyether ether ketone (CCF/PEEK), a thermoplastic composite, holds significant promise for applications in aerospace and automotive manufacturing. However, challenges such as temperature gradients during printing and insufficient fiber impregnation result in weak interfacial properties, making internal defects and failure mechanisms key areas of research. This study employs high-resolution synchrotron x-ray computed tomography (SR-CT) and digital volume correlation (DVC) to investigate the failure modes, defect evolution, and internal three-dimensional strain distribution in CCF/PEEK samples during tensile testing. The analysis reveals that strain concentrates in regions with dense continuous fiber distribution before material failure, while post-failure strain localizes within interlaminar cracks. Furthermore, defect evolution analysis suggests that extensive fusion and growth of defects around fibers may serve as precursors to material failure. These findings indicate that weak bonding at the fiber/resin interface is the primary cause of tensile failure in CCF/PEEK, providing valuable insights for failure prediction and optimization of molding processes. Highlights: Observation of CCF/PEEK failure modes using synchrotron radiation CT. Bulk cracks are concentrated in the interlaminar and fiber/resin interfaces. Significant difference in defect evolution before and after tensile failure. Strain concentration in the CCFs aggregation region predicts tensile failure.