| The automated fiber placement and in-situ consolidation process,which can significantly improve production efficiency and reduce manufacturing costs.can realize the synchronous manufacturing process of the thermoplastic composites.It has become a research hotspot in the aerospace field.As the composite materials continuously experience heating,melting,pressurization,cooling and consolidation steps during the forming process,complex temperature gradients and stress gradients will be generated inside the materials,which will cause residual stress and deformation of the components,and affect the geometric accuracy and mechanical properties.This thesis proposes a simulation model that can simulate the automated fiber placement and in-situ consolidation process of thermoplastic composites based on the process characteristics of in-situ forming process.The temperature field,stress field and springin deformation are analyzed in depth.The main research contents of this paper are as follows:Firstly,a transient heat transfer model of a two-dimensional temperature field based on hot gas heating was established.By establishing boundary conditions and forced convection coefficients,a two-dimensional finite element model was proposed to simulate the temperature field of the carbon fiber reinforced polyether ether ketone(CF/PEEK)prepreg during in-situ forming process.The influences of the hot gas temperature,the laying speed,and the initial temperature of the mold on the layers were analyzed.The placement platform of thermoplastic composites built by the laboratory was used to carry out the unidirectional laminate laying experiment.The correctness of the finite element model was verified by constructing a temperature field measurement system.The results show that appropriately increasing the initial mold temperature and laying speed,and reducing the hot gas temperature can improve the bonding and melting effects of the first layer and increase the laying efficiency.Secondly,the stress distribution and residual stress during the composite forming process were simulated based on the complete thermal-mechanical coupling model.The stress distribution laws of layers were obtained.And the influences of hot gas temperature,laying speed,laying pressure,and mold material on the residual stress of components were discussed.The results show that the residual stress decreases with the decrease of the hot gas temperature and the increase of the laying speed.The laying pressure nearly has no effect on the residual stress.The use of INVAR steel mold with a small thermal expansion coefficient can effectively reduce the residual stress.Furthermore,the generation mechanism for the residual stress of the thermoplastic composite components was analyzed from the three levels of micro,macro and global.Finally,based on the process characteristics of the in-situ consolidation process of composite materials,the ABAQUS user subroutine was develpoed to realize the co-simulation of the mobile heat source and pressure.The finite element model was employed to simulate the in-situ consolidation process of the angular composite material component.The validity of the model was verified by comparing with the spring-in deformation of the composite specimen after demolding.Furthermore,the influence of factors such as forming process parameters,component thickness and mold materials on the spring-in deformation of the component were studied.The essential reasons for the spring-in deformation of the composite component were explained from two aspects: the anisotropic thermal expansion effect of the composite material and the role of the mold in the forming process.Based on the proposed finite element model,the spring-in deformation of the composite lattice structure was predicted.The research results in this paper will provide theoretical guidance for the adjustment of forming temperature,stress and spring-in deformation of thermoplastic composite structures during in-situ forming process. |
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