Fracture Characteristics Of Concrete Under Reciprocating Load Based On DIC

Concrete is a kind of multiphase composite material,its failure and fracture mechanism is very complex.Due to the micro-cracks in the concrete structure during construction and operation,these cracks will gradually develop and even occur the instability of the structure under the action of environmental load.However,in addition to static load,concrete structure also bears complex dynamic load and repeated load,resulting in structural damage and fracture failure,resulting in the decline of bearing capacity and durability.Therefore,it is necessary to study the material properties of concrete under repeated or cyclic loading.In this paper,the characteristics of the fracture process zone of concrete three-point bending specimens in the cyclic loading process are studied through experiments.By analyzing the crack opening displacement(CMOD),the length of the process zone,the maximum displacement of the crack,the residual strain and the slope of the location shift distribution of the fracture process of the unloaded specimens under different loads,The characteristics of fracture process zone of three-point bending beam specimens under cyclic loading were summarized,and the correlation model was established by using ABAQUS software,and the correlation law was analyzed by comparing with the experimental results.The main work of this paper is as follows:(1)The digital image correlation method is briefly introduced,and the digital image correlation technology is used to measure and analyze the distribution law of crack opening displacement in the fracture process zone of concrete three-point bending beam under cyclic loading.Compared with DIC results,the reliability of DIC was verified,and the variation law of CMOD and other characteristics of concrete fracture process zone under reciprocating load was analyzed.(2)using DIC collected specimens at different times of the crack opening displacement(CMOD)and the process zone length,and DIC comes with 3 d analysis software are used to get the fracture process of different time zone strain contours,determine the existence of residual strain,by analyzing the CMOD,residual strain relations with unloading location,breaking process and combining the geographical distribution of slope,The law of residual strain and unloading position and slope of displacement distribution is summarized.(3)The p-CMOD curve law of specimens under different cycle times,the relationship between residual strain and CMOD corresponding to peak load of each cycle segment and cycle times were analyzed,and the energy dissipation under cycle load was analyzed by using the area and maximum width of cycle segment.(4)The extended finite Element(XFEM)module of Abaqus was used to conduct numerical simulation of fracture experiment of three-point curved beam,and equivalent analysis of softening curve under uniaxial load was carried out based on energy analysis method,and a numerical analysis method of concrete fracture considering residual strain was established,and compared with the test results.The relationship between residual strain and strain energy and crack propagation is obtained.