Peridynamic Simulation Of Fatigue Crack Propagation In Concrete

With the adoption of high-strength,light-weight concrete and high-strength steel bars,many structures are not only in a state of high stress,but also in a state of reduced self-weight and dead load.The proportion of fatigue load is relatively increased.In addition,the concrete structure is widely used in many occasions with more cycles and large repeated loads,such as marine structure,pressure structure,nuclear reactor containment and heavy machinery foundation,etc.,the fatigue failure of concrete structure is increasingly becoming a problem that cannot be ignored.Therefore,it is of great significance to study the damage process of concrete under fatigue load.The process of fatigue crack propagation is an important problem in the study of concrete fatigue damage.As a typical nonlocal field theory,peridynamics theory(PD)has the natural advantage of describing discontinuities such as crack propagation.In this paper,based on PD theory,a numerical model of concrete fatigue damage is established to simulate the process of concrete fatigue crack growth,which provides a new method for the durability study of concrete.The main work is as follows:1)Review of damage model and theory of peridynamicsThe basic idea of peridynamics theory is introduced.The PMB model and damage model of peridynamics theory are summarized in detail.The space discretization and time integration methods of peridynamics are studied,and the equations of motion of near-field dynamics with damping are given.It provides a basis for the establishment of PD model in the study of fatigue damage of concrete.2)Peridynamics model for fatigue damage analysis of concreteThe peridynamics model of fatigue failure is established based on the theory of damage mechanics and fracture mechanics.In the process of fatigue failure analysis,the model can simulate three stages of fatigue failure in a single model: crack initiation,fatigue growth and final failure controlled by quasi-static crack growth.According to the characteristics of high cycle fatigue analysis,the structural solution process based on cyclic block is introduced to improve the calculation efficiency.The critical damage factor is introduced to control the crack growth and improve the calculation accuracy.3)The meso PD model of concrete compositeIn order to simulate the micro structure characteristics of concrete,convex polygons are randomly placed to generate aggregates.The material properties of coarse aggregate,mortar and interface transition zone(ITZ)are given respectively by defining the parameters of interaction bond between different material points.The corresponding MATLAB program is compiled,which can generate the concrete meso PD model efficiently.4)Simulation of the whole fatigue crack propagation in concrete under cyclic loading by macroscopic and microscopic analysis methodAccording to the characteristics of different stages of concrete fatigue failure,the micro model and macro model of concrete are established to improve the calculation efficiency.In the stage of microcrack initiation,PD model of concrete composite material is used to simulate the process of damage evolution and microcrack formation;in the stage of macro crack formation,PD model of concrete material is used to simulate the process of macro crack growth;by introducing the discrimination mechanism of macro crack,the automatic conversion between micro model and macro model is realized.Based on the model,the whole process of fatigue crack growth of concrete under cyclic loading is analyzed.Based on the established fatigue damage analysis model of concrete,the influence of microstructure characteristics and stress level on the fatigue failure process of concrete is studied.The effects of random aggregate position,aggregate volume fraction and stress level on the fatigue crack growth mode and fatigue life of concrete are analyzed.The simulation results are in good agreement with the experimental results.The peridynamics model for fatigue damage analysis of concrete established above can effectively simulate the damage evolution,microcrack initiation and macro crack growth process in concrete by applying cyclic load,and realize the whole process simulation of fatigue failure of concrete,which provides a numerical method for studying the durability of concrete under fatigue load.