Virtual internal pair-bond model for quasi-brittle materials

The present multiscale investigation employs the initial and total fracture energy through a virtual internal pair-bond (VIPB) model. The proposed VIPB model is an extension of the traditional virtual internal bond (VIB) model. Two different types of potentials, a steep short-range potential and a shallow long-range potential, are employed to describe the initial and the total fracture energies, respectively. The Morse potential function is modified for the virtual bond potential so that it is independent of specific length scales associated with the lattice geometry. This feature is incorporated in the VIPB model, which uses both fracture energies and cohesive strength. With respect to the discretization by finite elements, we address the element size dependence in conjunction with the J integral. Parameters in the VIPB model are evaluated by numerical simulations of a pure tension test in conjunction with measured fracture parameters. We also validate the VIPB model by predicting load versus crack mouth opening displacement curves for geometrically similar specimens, and the measured size effect. Finally, we provide an example involving fiber-reinforced concrete, which demonstrates the advantage of the VIPB model over the usual VIB model.