Research On Defects And Process Of Unidirectional CFRP Mould Pressing

Nowadays,the world is faced with energy shortage and environmental pollution and other problems,forcing people to find ways to achieve the lightweight of aerospace,automobile and other fields of products,to reduce fuel consumption and protect the environment.Carbon Fiber Reinforced Plastic has been widely used in aerospace,automobile,rail transit and other industries because of its many excellent properties,such as low density,heat resistance,wear resistance and high specific strength.It has become a trend to replace metal materials for lightweight design of aircraft and automobile by this kind of composite material.However,CFRP has not been used in the automotive industry on a large scale because of its long production cycle,complex production process and lower molding speed than metal parts,which make it unable to meet the needs of mass and efficient production in the automotive industry.In this thesis,the molding process of unidirectional CFRP prepreg belt is studied to promote the lightweight design process of the automobile industry,which enables the largescale application of one-way composite materials in auto parts to meet the production needs of large quantities and high efficiency of the manufacturing industry.However,different from the molding of metal materials,carbon fiber composites in the molding of complex structure parts,due to its physical properties,such as anisotropy,thermodynamic coupling,etc.,is widely different from the traditional molding theory of metal materials.So exploring the forming theory of carbon fiber composites has been the focus of many scholars.In this thesis,hemispherical par ts are taken as the object of studying the full spread of unidirectional composites.The mould structure and electric heating system were designed,and the mould experiment platform was built.The molding experiment and finite element simulation analysis of the unidirectional CFRP prepreg strip were carried out.Through the structural design of the mold and the analysis of the temperature field,it is clear that the mold designed in this thesis can realize the temperature value needed in the processing area.It can provide the conditions for the next experiment of molding.The molding experiment and finite element simulation of single layer carbon fiber prepreg strip were carried out.The simulation model of macro and micro single layer CFRP was established,and the simulation analysis and experiment of unidirectional CFRP were carried out.The experimental results were compared with the simulation results.It is found that the similarity between the two features is high,which verifies the validity of the model.It was found that the single-layer unidirectional prepreg strip could not meet the forming requirements of the hemispherical parts and the overall full spread was poor.The main defects of the prepreg strip were the splitting of the fiber bundles and the fiber stacking in the curved fillet area.For different thickness of prepreg strip forming results.It was found that the smaller the monolayer thickness,the more uniform the fiber distribution,but the worse the full spread.Mold pressing experiment and simulation of a hemispherical part with laminated unidirectional carbon fiber prepreg strip are carried out.The effects of different thickness of single layer and different fiber structure on the quality of molded parts were studied.A threedimensional finite element model was established to simulate the forming of cross-intersection CFRP.Then,the unidirectional prepreg strip with different single layer thickness was molded to study the influence of unidirectional CFRP with different layer thickness on the molded quality.The results were compared with those of braided composites with the same thickness.The results show that the smaller the thickness of the unidirectional prepreg zone is,the larger the pore between the laminated fibers is,and the worse the density of the fiber distribution is.The larger the thickness of the unidirectional prepreg zone is,the smaller the interlayer fiber pore is,but the fiber stacking will occur.The inner surface quality of molded parts is superior to the outer surface quality.When the thickness of the hemispheric parts is smaller,the full spread of the unidirectional carbon fiber prepreg zone is better than that of the braided carbon fiber prepreg zone in terms of the distribution,arrangement and defects of the same prepreg zone.