Research On "Fiber Quasi-zero Stress" Rapid Forming Method For Carbon Fiber Reinforced Thermoplastic Composite

The excessive consumption of energy and the sustained destruction of the environment are huge problems that human development cannot avoid.The new energy and lightweight process are the mainstream trend of the development of the automobile industry.How to reduce the quality of the automobile,fuel consumption and exhaust emissions has become a research hotspot.As a leader in the field of new materials,composites are undoubtedly one of the best means to solve such problems.The advantages of light weight,high strength and hardness,and large specific modulus make carbon fiber reinforced composites became the most representative lightweight materials.Compared with thermosetting materials,thermoplastic composites have the advantages of environmental protection and recyclability.Compared with short fiber and long fiber products,continuous fiber products have better strength and stiffness,so thermoplastic continuous carbon fiber composites have very high research value.However,due to the poor toughness of carbon fibers,high viscosity of thermoplastic resin,and the lack of shear deformation ability of continuous unidirectional prepreg compared with woven fabric structure,wrinkling and corner fiber breakage always occur during forming.In view of the forming efficiency and forming quality of continuous fiber composite products in mass production,scholars have been looking for a fast and efficient manufacturing technology with fewer forming defects.Based on the demand of civil industry,and aiming at the forming problem of composite sheets,such as continuous fibers and thermoplastic resins,which have very different plastic deformability,the paper presents a "Fiber Quasi-Zero Stress"(FQZS)rapid forming method.The method utilizes quasi-isotropic One-Step inverse forming algorithm to analyze the complex three-dimensional composite products which cannot be flattened to realize the shape prediction of the blanks,and optimizes products rapidly into flattened free-form surfaces.The purpose of the FQZS is to solve the problems of stress concentration at the corner of mold,excessive elongation of local fibers,plastic fracture of internal fibers and surface forming defects caused by the undevelopable surface in the process of clamping.The new method ensures that under the cooperation of the resin,the continuous fibers inside the composite material are always in the state of unstretched so-called "Fiber Quasi-Zero Stress" throughout the molding process,and the deformation of the composite is almost entirely borne by the resin with high plastic deformation ability.The molding method of trimmed blank and corner reinforcement forming at the same time can effectively ensure the load-carrying capacity of the trimmed products.The trimmed part of the fiber is fixed and supported by unidirectional reinforcements.Based on One-Step inverse forming algorithm,the blank prediction and trimming iteration of products are simulated,the causes of forming defects of continuous carbon fibers are analyzed,and FQZS method is introduced to solve these defects.The feasibility and validity of the method are verified by the compression molding and quasi-static crushing experiments of box-shaped drawing parts made of carbon fiber reinforced polyamide 6 matrix composite.Through the research on the matching of different trimming gaps and reinforcements,the best forming mode of bearing capacity is determined: LSSC,which improves the surface quality of products without losing mechanical properties and greatly reduces the wrinkling degree of the surface.In this paper,warm-mold and hot material is used for molding,and the time of clamping and curing is very short(about 40 seconds).Compared with other molding methods,the production efficiency of FQZS composite sheet is obviously improved,and it is a molding method suitable for mass production in civil industry.