Research On Compression Molding Characteristics And Viscoelasticity For The Tackified Carbon Fiber Fabrics

Carbon fiber reinforced polymer(CFRP)composites have many advantages,such as excellent mechanical properties and low density.It is one of the effective ways to realize automobile lightweight.As one of the important links in the forming process of carbon fiber composites,the preforming process has a significant effect on the overall mechanical properties of the formed carbon fiber composites.Some complex-shaped parts are difficult to be made into near-net-shape fiber fabric preforms,so the tackifier is often used to enhance the styling effect of the fabrics.The application of the tackifier in the preforming process not only affects the dimensional accuracy of the composite parts,but also significantly affects its comprehensive mechanical properties.Therefore,this paper has carried out related research on the preforming process of the carbon fiber fabrics containing tackifier and its viscoelasticity characteristics in the forming process.First of all,in this paper,the tackified carbon fiber fabrics w ith different contents of the tackifier are used for the compression molding experiments,and the distribution patterns of different contents of the tackifier on the surface before and after the compression of the carbon fiber fabrics are characterized.The mechanism of thickness change during the compression process of the tackified fabric s is analyzed in detail,and the influence of the content of the tackifier on the formability of the carbon fiber fabrics is discussed.The results show that with the increase of the content of the tackifier,the initial thickness and compression time of the fabric s in the compression stage increase,the relaxation rate in the relaxation stage decreases,and the permanent deformation ratio in the rebound stage increases.F rom the styling effect point of view,the 4wt.% content of the tackifier has superior styling effect.Secondly,in this paper,the compression molding experiments of the carbon fiber fabrics are systematically carried out for four process parameters includ ing the compression speed,the maximum pressure,the holding time and the number of compression cycles in the preform,and the effect of the change of the process parameters on the thickness variation,stress relaxation capability and rebound deformation in the three stages of compression,relaxation and rebound is analyzed.The results show that decreasing the compression speed,increasing the maximum pressure and increasing the number of compression cycles can reduce the forming thickness and relaxation rate of the fabrics.The resilience of the fabric can be reduced by increasing the compression speed,reducing the maximum pressure,extending the holding time,and increasing the number of compression cycles.Finally,according to the creep recovery process in the viscoelastic deformation of the fabrics,the viscoelastic theoretical model of the fabrics containing the tackifier is established,and the correctness of the model is verified by the fabrics compression molding experiments.The related parameters of the model are obtained by fitting,the physical meaning of each parameter in the model is discussed in order to reflect the relationship between the physical parameters in the creep recovery process of the fabrics.A method for calculating permanent deformation and ultimate resilience by viscoelastic theoretical model formula is further established.With the increase of the content of the tackifier,the friction force and the adhesion force between the fibers increase,the resilience produced by fabrics deformation decreases,and the creep recovery time of fabrics increases.In view of the compression molding characteristics of the fabric s containing tackifier,this study is more close to the practical engineering applications.It is helpful to reduce the defects such as slip dislocation,internal buckling and excessive springback in the preforming process,which is of great guiding significance for the parameter adjustment in the actual preforming process.The study of viscoelastic properties of the tackified carbon fiber fabrics aims to provide some theoretical support for the high-performance composite liquid forming process.