Numerical Analysis Of Flow-compaction And Process-induced Residual Stresses Of Thick Composite Laminates

The resin flow and the fiber compaction of thick section composites during hot pressing process result in the internal component gradient distribution,which affects the internal residual stresses distribution and the mechanical properties of the composites.Therefore,in order to provide guidance for the analysis of residual stresses and process design for thick section composites,it is necessary to establish a flow-compaction and residual stresses coupling analysis method to analyze the effect of curing process on the flow-compaction behavior and residual stresses.By studying of cure state dependent viscoelastic constitutive model,the flow-compaction model,and the coupling residual stresses analysis method of the two models,a numerical method for the analysis of flow-compaction and residual stresses in thick section composites is put forward.Base on the numerical method,the development of residual stresses in thick section composites and the influence of flow-compaction on the component distribution and residual stresses are studied.The main results and conclusions are as follows:a)A cure state dependent viscoelastic constitutive model is developed,and the residual stresses in a thick-walled composite semi-cylindrical shell are analyzed.Based on the existing anisotropic thermo-viscoelastic constitutive model of composites,the viscoelastic characteristic parameters are proposed,which could control the viscoelastic properties of the composites.And the cure state dependent viscoelastic constitutive model is established based on the analysis of the characteristic parameters.Through the numerical analysis of the curing process for the thick composite,the rationality of the viscoelastic characteristic parameters and the correctness of the simplified model are verified.In addition,the development characteristics of the residual stresses of thick-walled composite semi-cylindrical shell and the influence of the section cooling process on the residual stresses areanalyzed.b)Based on the effective stress theory and Darcy's flow theory,a multi-field coupled numerical model is developed to simulate the flow and compaction of thick composite laminates,which is used to analyze the effect of the interface permeability on the flow-compaction process and component distribution.The flow-compaction process of AS4/3501-6 composites is analyzed,and the correctness of the model is verified by comparing with the results reported in the literature.A thick cross ply composite laminate model with an interface layer is built,and is used to analyze the effect of the interface permeability on the flow and compaction process of the thick cross ply composite laminate.The results show that,an interface layer with low permeability impedes the resin flow in the thick cross ply composite laminate,and result in the decrease of fiber volume content.c)Flow-compaction and residual stresses coupling numerical analysis for a thick section composite laminate is developed.Based on the results of the cure state dependent viscoelastic constitutive model and the flow-compaction analysis,a numerical analysis method which couples the flow-compaction and residual stresses of the thick composite laminate is established by using the micromechanics model.The influence of gradient distribution on the residual stresses distribution in the unidirectional laminate and the cross ply laminate is calculated.The results show that the gradient distribution of the components leads to the increase of tensile stress inside the unidirectional laminate,and the effect of the residual stress on the cross ply laminate is not obvious.