Numerical Simulation Of Damage And Fracture Of Concrete At Meso-Scale Based On Cohesive Crack Model

Concrete is widely used in building structures,the tumble down of the bridge and high building is often caused by the failure of key structure because damage evolution,and this is a multi-scale mechanics problem cross materials,components to structures.The damage research of concrete material has fundamental significance in engineering disaster prediction and protection.This paper reviewed the damage research method of quasi brittle material,mesoscopic mechanics model is presented to be a powerful method for concrete damage research by using numerical simulation.Concrete is a kind of complex multiphase composite material,in the traditional damage research field it is usually assumes to be homogeneity,but at mesoscopic level,the mechanical performance of concrete depends on the properties of its internal structure.The initiation and development of crack are significantly affected by the internal structure,which is the direct reason cause damage in concrete.Mesoscopic model can consider the internal structure of concrete and become a rapidly developing tool to study the damage at mesoscopic scale.Precisely because of this viewpoint,the paper adopts a mesoscopic model of concrete to study mesoscopic damage behavior and damage mechanism.At the mesoscopic level,concrete is considered to be three-phase composite materials,it is composed of aggregate,mortar and interface transition zone(ITZ)between aggregate and mortar.This paper uses an improved algorithm realize the random place of circular aggregate,finish mesoscopic model of concrete.The key in using mesoscopic model research damage is the reasonably describe the crack initiation and development.Base on this,in the paper we use the cohesive property describe the interaction of material interface.In the process of modeling,the mesoscopic concrete specimen is firstly meshed by traditional elements,then zero thickness cohesive elements are inserted at the potential of crack initiation and extension zone,and the traction-separation debonding property is used for zero thickness cohesive elements,after these steps the mesoscopic cohesive crack model of concrete is developed.The initiation,growth and coalescence of micro cracks are tracked throughout the simulation by using the debonding and connection of cohesive elements,by this way two damage parameters micro crack density and crack coalescence are defined to represent the damage level and failure process of concrete.Using the present model,the damage and failure process under uniaxial tension and uniaxial compression are simulated.In the case of uniaxial tension condition,combine the defined damage parameters and stress-displacement curve the damage progress behavior and fracture energy dissipation behavior of difference failure models are analyzed;In the case of uniaxial compression condition,the fracture behavior of specimens under no loading face constraints and fully loading face constraints are simulated,the internal failure mechanism of different failure models are analyzed.Through contrast and analysis the deformation of cohesive elements under different loading condition shows under uniaxial tension normal open deformation is the mean form,but under the uniaxial compression the tangential dislocation deformation is the mean form.This means the failure of concrete in differernt condition are controlled by different damage mechanism.