A novel XFEM cohesive fracture framework for modeling nonlocal slip in randomly discrete fiber reinforced cementitious composites

We develop and implement a new nonlocal crack-bridging model for evaluating toughening and strengthening mechanisms of fiber reinforced cementitious composites. The quasibrittle fracture of cement matrix is characterized by XFEM-cohesive crack framework. To explore fiber-bridging mechanism, the horizontal fiber phases corresponding to different embedding length are superimposed on the near-crack region of the matrix phase, while an effective homogeneous Cauchy medium is assumed outside the multiphase region. The sliding interface for each fiber phase is described by a slip field, leading to a new nonlocal slip model being proposed which can be used to treat arbitrary fiber distributions. This model is formulated in a variationally consistent framework. In this study, it is verified that the toughening effect is induced by the interfacial shear stress rather than the fiber tensile stress. Prior to evaluate new problems, the capability of the proposed model is validated to reproduce consistent fracture behaviors with the experimentations. It is concluded from our systematic studies that a higher fiber modulus leads to a higher loading capacity, but not a higher composite toughness, while unaffects its residual strength. It is found that the enhancing interfacial strength has improved the composites toughness dramatically, but has limited contribution to the strengthening effect.