Experimental Investigation On Fracture Behavior Of Concrete Under Three Point Bending Test And Numerical Simulation

The concrete is a three-phase composite material composed of coarse aggregate,cement paste and the bonding surface between the two.General studies have shown that the interface between concrete aggregate and cement is a weak link,which has an important effect on the mechanical properties of concrete.Aggregate is randomly dispersed in hardened cement paste.Aggregates and cement pastes can be regarded as homogeneous materials with uniform mechanical properties.However,the mechanical properties of the bonding interface are complicated.As the cement slurry hardening and shrinking,the interface of water(slurry water loss)and the evaporation of water loss,some from the surface,micro-cracks,stomatal will compete in the first combination of the two appearances,these defects will be under the action of external load through into cracks.The expansion of the formation of macroscopic cracks will develop as well as finally the phenomenon of low stress brittle fracture.Especially in the study of hydraulic dams,the occurrence of engineering accidents will cause great economic loss to the country and the people,and the concrete brittle and brittle is particularly noticeable.Therefore,the fracture mechanics of concrete since its birth date is always a subject matter of concern.This paper introduces the history about the development of concrete fracture mechanics summarizing the test methods and numerical simulation methods for studying the fracture of concrete.Several important parameters of concrete type?fracture are simulated by three-point bending beam test method to determining the fracture performance of concrete.The results show that fracture energies obtained by RILEM recommendation are higher than that obtained by the other two methods.When the ratio of the lowest load at the descending part of the curve to the peak load(Pmin/Pc)is lower than 0.04,the errors of the fracture energies obtained by the actual load-deflection curves and that obtained by the extended curve are less than 5%,which could provide a reference for the implementation of the fracture tests.The fracture parameters determined by using the Equivalent Fracture Model and the Two Parameter Fracture Model are close.The fracture toughness increases as the increase of compressive strength of concrete.Empirical formula is built to determine the fracture toughness by using the compressive strength.Based on ABAQUS,the numerical methods of three kinds of simulated crack propagation processes including cohesive force model,virtual crack closure technique and extended finite element method are discussed.The analysis of the double cantilever beam(DCB)model shows that the three methods can complete the simulation of crack propagation,in which the extended finite element method can achieve free expansion along any paths,showing more excellent performance.Finally,based on ABAQUS built-in extended finite element method,the crack initiation process of three-point curved concrete beams are simulated.The main parameters of numerical model are discussed.Through simulation of large-size specimen,it is found that the crack propagation can be divided into three stages: Pre-expansion stage,stable expansion and damage accumulation stage,instability expansion.When the span is increasing to 1200 mm,due to the innegligible shearing effect,there are ?,?? complex type cracks.It is hoped that it can provide reference for the study of concrete fracture mechanics.Finally,the main contents of this paper are summarized,and the areas and research methods which need to be further expanded are pointed out.