Study Of The Damage Process Of ECC-concrete Bonded Interface Based On Peridynamics

The use of engineered cementitious composites(ECC)for the reinforcement and repair of concrete structures has promising applications.However,the mechanical properties of the transition zone at the bonded interface are critical for the composite materials,but the nonlinearity of the material properties poses difficulties for the conventional mechanical analysis based on the classical continuum mechanics theory.Peridynamic theory is a nonlocal model that considers long-range actionsuses spatial integral equations instead of the spatial differential equations of the traditional continuous medium theory to formulate the motion of a body.It does not require the derivation of the displacement field of the body,thus avoiding the singularity of the differential calculation procedure of the traditional continuous medium theory when dealing with discontinuities such as fractures.In this study,a PD interface model based on the energy method is constructed in the framework of the peridynamic theory,and a full-process simulation of the failure behavior of the bonded interface between ECC and concrete is performed according to this model.The main contents and research conclusions of this study are summarized as follows:(1)The interface model based on energy method is used to analyze the behavior of the bimaterial interface under tensile and shear loads.By comparing with the finite element solution,it can be found that the PD solution is basically consistent with the finite element solution at a distance from the interface area,and there is a certain difference in the interface area,but the error of the PD solution is within 10%.Secondly,the peridynamic radius and grid spacing used in this study are determined by simulating the cement matrix without fibers and concrete.The peridynamic radius δ is 4mm and the grid spacing Δx is 1mm,which can meet the calculation requirements and calculation effectiveness of this study.(2)Using the constructed model,the damage process of the bond interface between ECC and concrete is simulated.By simulating the crack propagation process of composite members under splitting tension load and bending load,it is verified that the crack resistance of fibers in ECC and the existence of ECC layer can effectively disperse the cracks in concrete.It further reflects the reliability of the interface model established in this study and the significant advantages of using PD theory to simulate the interface damage problem.(3)By simulating the laminated beams with different fiber volume fractions and different ECC layer thicknesses,it can be found that when the fiber volume fraction increases to a certain value,the number of cracks does not increase significantly,because there is an optimal value for the fiber volume fractions.Like the fiber volume fractions,the thickness of the ECC layer also has a critical value.When the proportion of the ECC layer exceeds the critical value,diagonal cracks will appear in the bending and shearing area of the laminated beam.(4)By studying the crack expansion path of composite plates under biaxial loading,it is known that the fibers affect the crack expansion path by influencing the stress wave propagation path.The crack expansion paths for different load ratios show that the load ratio has a strong influence on the crack expansion.In this study,PD theory was applied to analyze the damage process of ECC and concrete bonded interface,and the crack propagation path of concrete and ECC composite members was obtained under different conditions,which has positive significance for promoting the application of PD theory and studying the fracture behavior of ECC concrete bonded interface.