Strengthening mechanism of steel fiber in UHPC: A new fracture phase field model

The engineering optimization of ultra-high strength concrete (UHPC) requires urgent exploration of the strengthening mechanism of steel fiber in UHPC and the establishment of an effective simulation model. In this study, we propose a new fracture phase field model that considers the fracture energy of the interface between steel fiber and UHPC matrix. The model is utilized to conduct uniaxial tensile numerical simulations of 3D UHPC incorporating steel fibers, and a comparative experiment is conducted to validate the proposed model. The results display a notable agreement between the simulation and experiment. It is found that the tensile strength and residual strength of UHPC increase with steel fiber volume content and decrease with steel fiber diameter. The inclusion of steel fibers in UHPC results in more intricate crack patterns during the fracture process. The above results can be attributed to the debonding occurring at the interface between the steel fiber and the UHPC matrix which dissipates additional energy and thus enhances the UHPC. This work establishes a theoretical foundation for UHPC performance design and the development of effective simulation methods.