Investigation On Inter-ply Slipping Behavior Of Carbon Fiber Prepreg And Its Application In Hot Diaphragm Forming

The hot diaphragm forming process of composite is a process of multi-physical field coupling,large deformation and anisotropy,which may produce wrinkling,tearing and other defects in actual production.In order to understand the causes of these defects,it is necessary to accurately grasp the forming mechanism.In the hot diaphragm forming,the forming mechanism of prepreg includes shear deformation,local resin flow,inter-ply slipping and so on.Among them,the inter-ply slipping is directly related to the wrinkling of the prepreg,and when the inter-ply slipping is blocked,it often affects the residual stress,surface quality and mechanical properties of the cured parts.However,the existing inter-ply slipping model between prepreg and prepreg cannot accurately describe the inter-ply slipping behavior in the whole forming process because the influence of relative slipping displacement is not taken into account.Therefore,the main purpose of this paper is to establish an inter-ply slipping model considering the influence of relative slip displacement and process parameters,to build a hot diaphragm forming system and to establish a finite element simulation model of hot diaphragm preforming.The accuracy of the developed interply slipping model is verified by the comparison of experimental and simulation results.In view of the above research objectives,the research problems are decomposed step by step,and the main research contents are as follows:In the aspect of experiment,the DSC test of the prepreg was carried out,and the temperature of the hot diaphragm preforming of this prepreg system was determined to be below 90?.Based on the pull-through test method,a set of inter-ply slipping testing system was designed.Using this system,the slipping properties of different contact interfaces(prepreg/prepreg,prepreg/release film,release film/diaphragm)were tested,and the effects of temperature,normal pressure and rate on tangential stress were analyzed.Based on the basic principle of hot diaphragm forming,a hot diaphragm forming system was built,including heating system,vacuum system,testing system and forming tools.Using the hot diaphragm forming system,hot diaphragm forming experiment was carried out,and the influence of temperature on the forming result was analyzed.Finally,it is obtained that the optimum temperature range of hot diaphragm preforming is between 70? and 80?.Through the uniaxial tensile test of unidirectional prepreg and diaphragm,the mechanical properties of prepreg and diaphragm at different temperatures were obtained.In the aspect of mathematical model and finite element simulation,for the test results of inter-ply slipping,a "three-stage" inter-ply slipping mechanical model considering the influence of relative slip displacement and process parameters(temperature and normal pressure)was established by inductive analysis.For diaphragm,based on continuum mechanics and virtual work principle,an isotropic hyperelastic constitutive model considering the effect of temperature was developed.The model was compiled into the finite element simulation model of diaphragm cover deformation by Abaqus subroutine UHYPER.The comparison between the diaphragm cover deformation experiment and the simulation results shows that the model has high accuracy.For the prepreg,the model parameters of the prepreg at different temperatures were calculated by using the transversely isotropic plane stress model.Finally,the simulation model of hot diaphragm preforming is obtained by compiling and merging the inter-ply slipping mechanical model through the Abaqus subroutine FRIC.By comparing the simulation and experimental results of hot diaphragm preforming with three-layer and fourteen-layer prepreg laminate,it is verified that the proposed "three-stage" inter-ply slipping mechanical model and hot diaphragm preforming finite element model have high accuracy.Using the developed hot diaphragm preforming simulation model and Taguchi(Taguchi)analysis method,the effects of tangential behavior(friction coefficient)between die/diaphragm,diaphragm/diaphragm and prepreg/prepreg on the wrinkling index of prepreg were compared.At the same time,the effect of temperature on the hot diaphragm preforming process was analyzed.The "three-stage" mechanical model of inter-ply slipping of carbon fiber prepreg established in this paper enriches and improves the existing inter-ply slipping model of prepreg,and can be used in the preforming simulation of prepreg such as hot molding or hot diaphragm forming process.The hot diaphragm preforming simulation model can be used to determine the early process parameters and optimize the subsequent hot diaphragm preforming process,which lays a solid foundation for the hot diaphragm forming theory.