Research On Progressive Damage And Bonding Repair Of Perforated Composite Laminates

Carbon fiber reinforced composites(CFRP)are especially popular in aerospace,automobile and other fields because of their high specific strength,high specific stiffness,excellent fatigue resistance and corrosion resistance.With the rapid development of composite technology,its design method and manufacturing technology have become increasingly mature and perfect.As the most commonly used composite structure,laminates inevitably cause structural damage due to impact,extrusion or environmental conditions in practical applications.It is not economical to replace damaged composite components to restore structural integrity.It is necessary to repair damaged composite laminates in time.Bonding repair is a common repair method.Therefore,the ultimate strength prediction and progressive damage propagation characteristics of composite laminates with holes and bonding patch configurations are studied in this paper.The main research work is as follows:Firstly,based on the damage constitutive model of continuum damage mechanics(CDM)and the Cohesive Zone Model(CZM),a three-dimensional progressive damage theoretical model of composite laminates and bonded repair structures is established.The user material subroutine UMAT based on three-dimensional strain damage failure criterion is compiled.The stiffness reduction and damage calculation are carried out by calling UMAT through ABAQUS platform.The progressive damage of laminates takes into account three damage modes: fiber,matrix and delamination,and the stiffness degradation chooses a non-linear reduction mode;the constitutive relationship of the adhesive layer chooses a bilinear model;the secondary nominal stress criterion under the mixed mode load is chosen for the initial damage;and the exponential criterion considering the energy release rate is chosen for the damage propagation criterion.Secondly,three-dimensional progressive damage analysis model is used to simulate the ultimate bearing capacity of composite laminates with holes under uniaxial tension and compression loads.The accuracy and validity of the damage analysis model are verified by comparing the simulation results with the experimental data.On this basis,the influence of aperture size and shape on ultimate strength of laminates is further studied.Thirdly,biaxial tension tests of cross-shaped perforated composite laminates with load ratios of 1:1,2:1 and 3:1 were carried out.The ultimate load and progressive damage were calculated and analyzed by using the finite element model corresponding to the test.By comparing the calculated results with the experimental data,the damage propagation characteristics and the experimental phenomena are analyzed correspondingly,which verifies that the analytical model is suitable for the progressive damage study of laminates under biaxial tensile loading.The damage evolution characteristics of rectangular and square laminates under biaxial tension are further studied by using the model.Finally,uniaxial tension tests were carried out on the specimens of double-sided bonded laminates.A finite element model corresponding to the test was established.The ultimate strength and progressive damage of the two patching configurations were calculated and analyzed.The damage propagation characteristics of laminates and adhesives under uniaxial tension were studied.The comparison between the simulation results and the experimental data shows that the damage analysis model is still applicable to progressive damage analysis and ultimate strength prediction of double-sided bonded laminates under uniaxial tension.