Meso-failure Characteristics Of Geopolymer Composites Based On Cohesive Zone Model

Geopolymer is a multiphase composite material prepared by Al-Si stimulated materials,activators and aggregates according to a certain ratio.Similar to ordinary concrete materials,geopolymer materials have low tensile strength,while the incorporation of fiber can effectively improve its ductility.The macroscopic fracture and failure of geopolymer or fiber-reinforced geopolymer materials under load is essentially caused by the meso-damage evolution at the interface of multiphase materials.Therefore,how to introduce the interface constitutive into the finite element calculation framework is the key to analysis the whole failure process of multiphase material.In consideration of the successful application of cohesive zone in the quasi brittle material,this paper combined the extended finite element method with the framework of cohesive zone model to analysis the macroscopic fracture process of geopolymer concrete,a constitutive model is developed by means of ABAQUS subroutine,which can explicit describe the process of fiber debonding,slipping and pulling friction.The failure process of fiber-reinforced geopolymer was simulated and analyzed in meso-scale,specific research contents and conclusions are as follows:(1)Under the frame of XFEM and CZM,try adopting various forms of CZM model of geopolymer concrete to simulate the instability and failure of crack initiation and extension,and even the whole failure process under bending loads,based on double K fracture model calculate the crack instability fracture toughness and fracture toughness,the results were compared with the experiment,obtained the best CZM model for describing the geopolymer concrete fracture characteristics,reveals the evolution regularity of geopolymer concrete fracture characteristics.(2)The subroutine interface that can realize the cohesive zone model in ABAQUS is discussed,and the expression form of the cohesive element and its constitutive relation of element and material in ABAQUS is summarized.The displacement energy coupling relationship is introduced on the basis of the classical bilinear cohesive zone model,and the flow structure of UEL subroutine is designed by FORTRAN language.Combined with the rich pre-processing script interface in ABAQUS,it is convenient to build zero-thickness cohesive element in geometric models.(3)Put forward a kind of shear composite cohesive constitutive relation which can explicit describe the process of fiber debonding,slipping and pulling friction,by insert a zero thickness cohesive element at the interfaces as a transfer of the stress,the finite element model of interface coupling between fiber and geopolymer matrix at meso-scale is presented intuitively,and combined with the unit test proved that it can accurately reflect the loading and the damage processing of interface element.The mechanical properties of single fiber pullout process are simulated and the influencing factors are systematically analyzed.The calculation method of fiber distribution algorithm is given,and the failure process of multi-fiber specimens under bending stress is simulated.The results show that the cohesive zone model combined with UEL subroutine can accurately simulate the stress process and damage state of fiber and matrix by setting reasonable model parameters.