Effect of unit cell structure and braiding angle on the tribological properties of carbon fiber/epoxy 3D braided composites

The ambiguous correlation between three dimensional (3D) braided structures and tribological properties in epoxy resin (EP) based composites poses significant challenges in developing high wear resistant materials. To address this, we fabricated carbon fiber/EP braided composites featuring distinct unit cells (the inner unit cell and the surface unit cell) and braiding angles (10 degrees, 20 degrees, 30 degrees, 40 degrees). Tribological assessment through ball-on-disc testing against steel counterparts at ambient temperature indicated that braided composites featuring the inner unit cell as the friction surfaces attained an optimal coefficient of friction (COF) of 0.25. By integrating experimental characterization and finite element analysis, we initiated a unit cell level analysis, demonstrating that composite wear originates from crack propagation induced by cyclic plastic deformation. The interwoven carbon fiber architecture substantially enhances the matrix's resistance to plastic deformation. In composites with large braiding angles, especially at 40 degrees, tighter fiber interlacing effectively restricts deformation under cyclic loading, thereby enhancing wear resistance. Notably, inner unit cell structure exhibits superior wear resistance compared to surface cell structure owing to its high carbon fiber content. Through systematic tribological evaluation under equivalent fiber content conditions, the wear rate of braided composites is significantly reduced compared with that of unidirectional composites (191.98 x 10-6 mm3/(N center dot m)) and pure EP (330.34 x 10-6 mm3/(N center dot m)), reaching the lowest value of 8.8 x 10-6 mm3/(N center dot m), conclusively demonstrating the superior tribological performance enabled by three-dimensional fiber architecture. The results of this work provide new insights for analyzing, designing and manufacturing high wear resistant composites.