Simulation Research On Mechanical Properties Of 2D Braided CFRP Based On Dynamic Change Of Braiding Angle

In recent years,with the application and demand of composite materials in the automotive industry increasing year by year,research on composite materials has also received extensive attention.Compared with traditional experiments,simulation simulation has the advantages of low cost,flexible parameter change,short cycle and high efficiency,and is one of the main means to study the mechanical properties of composite materials.The mechanical properties analysis of 2D braided carbon fiber reinforced composites(braided CFRP)is generally carried out from two scales,mesoscopic and macroscopic.The macroscopic mechanical properties of braided CFRP are determined by its mesoscopic structure.The mesoscopic model is mainly composed of fiber bundles and epoxy resin matrix,and the macroscopic model is assumed to be a continuum model.The braiding angle is an important geometric parameter of braided CFRP mesostructure,and its size affects the mechanical properties of the material.Under the action of off-axis tensile load,the braiding angle of braided CFRP changes in real time with the deformation of the material.The mesoscopic model can simulate the braided structure to obtain the effect of the change of braiding angle on deformation and damage.For the macroscopic model,the change of the angle causes the properties of the material to be no longer the initial set value,but changes continuously with the loading process,ignoring the dynamic change of the braided angle,which directly affects the accuracy of the simulation of the macroscopic mechanical properties of braided CFRP.Therefore,based on the progressive damage evolution theory and finite element simulation,this paper conducts the microscale simulation of braided CFRP,and through the off-axis tensile test of braided CFRP and the dynamic change measurement of the braid angle,the damage failure mechanism of the material and the change law of the braid angle are revealed.Based on the microscopic simulation and macroscopic test,the influence parameters of the braiding angle are introduced to improve the macroscopic material model,and the macroscopic simulation research considering the real-time change of the braiding angle is carried out.Firstly,the fabric software TEXGEN is used to establish the geometric model of the woven CFRP unit cell,the component material fiber bundle adopts the orthotropic constitutive model based on continuous damage mechanics,and the resin matrix adopts the ductile damage constitutive model based on Lin constitutive.Associated with the VUMAT material subprogram,a 2D braided CFRP meso-finite element model including fiber bundles and epoxy resin matrix is established by the finite element software ABAQUS to realize the failure simulation of the braided CFRP meso-structure.Secondly,through the off-axis tensile test of the braided CFRP with different layers,the number of layers of the test piece that fully reflects the mechanical properties of the braided CFRP is determined,and the theoretical value of the dynamic change of the braiding angle is obtained according to theoretical assumptions.The dynamic change curve of the braid angle during the test loading process is obtained by processing,and the dynamic change of the braid angle is measured on the finite element model of the mesostructure.The results are analyzed to obtain the change law of the braid angle during the loading process.Finally,by establishing the mesoscopic unit cell finite element model of different initial braiding angles,the variation law of elastic parameters with the initial braiding angle is predicted,the sensitive items of elastic parameters are determined,the parameters affecting the braiding angle are introduced,and the relationship between the elastic parameters and the sensitive elastic parameters and strain is established.Based on the functional relationship,the macroscopic failure model of braided CFRP including the parameters affecting the braid angle is established,and the macroscopic simulation study considering the real-time change of the braid angle is carried out,and the accuracy of the macroscopic simulation of braided CFRP is verified by comparing the test curves.