Effect of fiber roughness on interfacial friction of fiber reinforced ceramic matrix composites

Interfacial friction plays a crucial role on mechanical behaviors of fiber reinforced ceramic matrix composites (FRCMCs), such as matrix cracking, damage evolution, and fracture, and the fiber surface roughness has been shown to enhance the interface friction. However, the influence of interphase thickness and residual stress on the friction enhancement of fiber roughness was neglected in previous works. Therefore, in this paper a thoroughly theoretical model is established and the additional radial stress is derived to intuitively reflect the contribution of fiber roughness to the interfacial friction. The results indicate that the interfacial friction can usually be enhanced by increasing the fiber roughness and reducing the interphase thickness, which however is severely overestimated by more than 5 times by the previous models. Moreover, the residual stress and fiber axial stress have a nonnegligible effect on the contribution of fiber roughness. For a given fiber axial stress, the residual stress that is too large or too small will weaken or even eliminate the contribution of fiber roughness, and only when the residual stress is within a proper range, can the fiber roughness play an effective role. On the other hand, for a given target load and ambient temperature, a critical fiber roughness that can enhance the interfacial friction is analytically derived. This work can provide valuable insights into the design of fiber roughness and interphase thickness for FRCMCs.