An Improved Park-Paulino-Roesler (PPR) Cohesive Model Considering Rate-Dependent Characteristics and Frictional Behavior of Brittle Materials

To characterize the rate-dependency and frictional behavior of quasi-brittle interface material, a coupling rate-dependent and friction interface model improved from the Park-Paulino-Roesler (PPR) cohesive model, is proposed and validated in this paper. Based on the potential function, this novel coupling model forms the basic relationship of traction-displacement within the interfaces, in which rate effect and friction behavior are considered by constructing a rate-sensitive item and smooth friction term, respectively. Specifically, governing equations for typical mode I and mode II crack formation, as well as for normal and tangential directions, are established, and the model includes a complete unloading/reloading mode for the complex loading situations. To validate this model, the 3D simplified shear test of the anchor rod and mortar block model and a three-point bend test of the composite concrete-FRP beam with different loading rates are established to verify the engineering availability, considering different loading rates and friction coefficients. The results show that shear and tensile behaviors of brittle material in numerical models and laboratory tests are similar in the fracture initiation and propagation characteristics. The proposed model can reflect not only the elastic, softening, and residual stages, but also the strength rate-related effects and friction effects of interface materials. This provides a comprehensive solution for describing the complex mechanical behavior of quasi-brittle materials subjected to tensile and shear loads.