Tensile Properties Of Chopped Carbon Fiber Reinforced Vinyl Ester Resin Sheet Molding Compound

With the gradual improvement of people's requirements on the quality of automobiles,the addition of various types of additional devices has led to an increase in the weight of automobiles,which has brought about a series of problems such as fuel consumption and pollution.Therefore,lightweight has become the main target and driving force for the development of the automobile industry in the future.With the advent of the new material era,the limitations of traditional single-phase materials have limited their application space.On the other hand,composite materials with excellent performance and wide application are rapidly developing.The carbon fiber-reinforced composite materials known for their lightweight,high strength and excellent performance have also become the focus of current research.Sheet-type molding compound(SMC)is a composite material in which a short-cut fiber or a mat-reinforced thermosetting resinreinforced sheet is placed in a hot mold for press molding.The degree of automation is high,and a complex-shaped member can be molded at one time.The surface of the products is bright and clean,so it has a broad application prospect in the field of automotive lightweight.With the gradual industrialization of carbon fiber,the cost of producing carbon fiber is reduced.Carbon fiber reinforced lightweight materials are widely used in the transportation industry,and short-cut carbon fiber reinforced vinyl ester resin sheet molding compound(CF-SMC)is rarely researched.In this paper,the tensile properties of CF-SMC composites were analyzed by finite element analysis and experiments,in order to provide theoretical support for the application of CF-SMC composites in automotive lightweighting.Through the secondary development of ABAQUS using Python language,a twodimensional plane strain model of randomly distributed short-cut carbon fibers was generated,a representative volume element was established,and Hypermesh was used in meshing to ensure representative volume units under periodic boundary conditions.Finite element analysis of the tensile properties,and analysis of the effect of carbon fiber length on the tensile modulus of the CF-SMC composite material were analyzed,obtained that as the length of the carbon fiber increases,the elastic modulus of the CF-SMC composite gradually increases.The law of increase,and the slope of the increase in tensile modulus appear to increase first and then slow down.When the fiber length is 12 mm,the tensile modulus of the sheet molding plastic increases by 91.3% relative to the fiber length of 2 mm,indicating an increase in fiber length is very meaningful for the increase in tensile modulus is significant.When the fiber length is short,the stress concentration at the end of the fiber is relatively obvious with respect to the long fiber,and with the increase of the fiber length,the stress concentration at the fiber end is relieved,the fiber axial stress gradually becomes larger.The stress distribution of the uniformly distributed fibers is significantly greater than that of the deflecting direction.A meso-mechanical model is designed to study the influence of the distance of the carbon fiber ends on the stress concentration of the CF-SMC composite.As the increase of the fiber ends,the concentration of stress increases first and then decreases.In order to improve the interfacial properties of carbon fiber and resin,the interface modification of carbon fiber was carried out by using acrylamide grafting method,acrylamide “migration method”,and sizing agent method to determine the interface treatment method for CF-SMC composite materials.Preparation of sizing agent was selected for carbon fiber interface modification;12mm length of carbon fiber as a reinforcement body was researched for the best molding process,and determined that the press pressure is 8MPa,the mold preheat temperature 120 °C,molding temperature 145 °C,holding time 180 s,exhaust twice,each time for 10 s,the materials were released on high temperature.The mechanical properties of the sample were tested,and the micromorphology and tensile modulus were analyzed.After adjusting the forming pressure,the tensile modulus of the sheet-shaped molded plastic increased by 61.9% when the fiber length was 12 mm relative to the fiber length of 2 mm.Comparing the numerical analysis results with the experimental results,when the fiber length is less than 7.7mm,the error between the simulated and experimental values is about 20%,which is within the acceptable range of the error.However,with the increase of the fiber length,the dispersibility is reduced,the interface infiltration is poor,the interface bonding strength is affected,and the error between the experimental value and the simulated value is larger,which demonstrates the rationality and correctness of the model.This work provides theoretical and experimental evidence for the application of sheet molding compounds in the automotive lightweight industry.