Research On The Strength Of Carbon Fiber Reinforced Plastics Bolt Joint And Finite Element Analysis

With the reduction of raw material cost of carbon fiber reinforced plastics(CFRP),the improvement of molding technology and performance,the application of CFRP in automobiles is one of the main development trends.However,the design and application of carbon fiber composites involve not only involve structural integration,but also consider the joint design.The design and strength analysis of the joint structure are often more complicated than that of metal materials because of the anisotropic mechanical characteristics of composite materials.Mechanical joint,adhesive and hybrid joint are common connection methods.The mechanical joint is the most commonly used joint method because of convenient for disassembly,easy to maintenance,and low interface requirements.In this paper,the bolted structure of CFRP was taken as the research object.The experimental and finite element analysis methods were used to research the squeeze performance of the bolted structure,which provides a reference basis for the design of the CFRP impact beam joint.The main research contents were as follows:(1)Evaluation and analysis of bearing strength test and failure mode of CFRP singlelap bolt joint structure: The effects of bolt torque and connection geometry on the failure load and failure mode of the joint structure were analyzed,and the reference values for the design of the double-lap bolt joint structure were obtained.The reference values of the structural design are bolt torque of 9 N·m,hole diameter of 6.1 mm,edge distance to diameter ration of 3,width to diameter ration of 6,and washer size of 17.8 mm.At the same layup ratio [(0°)46%/(±45°)46%/(90°)8%],the increase in thickness can increase the failure load,but the bearing strength has not improved.(2)Evaluation and analysis of bearing strength test and failure mode of CFRP doublelap bolt joint structure: The effects of bolt torque and connection geometry on the failure load and failure mode of the joint structure were analyzed,and the reference values for the design of the double-lap bolt joint structure were obtained.The reference values of the structural design are pre-tension force of 9 N·m,hole diameter of 6.1 mm,end distance/hole diameter ratio of 3,plate width/hole diameter ratio of 6.At the same layup ratio [(0°)46%/(± 45°)46% /(90°)8%],the increase in thickness can increase the failure load,but the bearing strength has not improved.(3)In Abaqus finite element software,a VUMAT subroutine was written,which defined an improved 3D Hashin criterion and integrated Tan and Tserpes material stiffness degradation model.A reliable finite element model of CFRP bolt joint structure was established for analysis.The comparative analysis between the finite element analysis results and the experimental results verified the reliability of the finite element model.(4)For the CFRP car door impact beam,a lay-up scheme for bolt joint test was selected.Fibersim was used to analyze the spreadability of carbon fiber prepreg on the impact beam forming mold,and the layup effect of prepreg was optimized.Based on the experimentally obtained reference values for the design of the bolted joint structure,the joint area of the CFRP impact beam was designed.The three-point bending test and simulation analysis were performed on the impact beam.It was found that the experimental failure load reached 8027 N under the optimal lay-up scheme(0/45/0/-45/0/45/90/-45/0/45/0/-45/0)s,and no obvious damage occurred at the bolted joint of the impact beam.The assembly schemes for door accessories such as door outer panels,window frames,impact beam,door locks were designed.Finally,the door assembly schemes was performed.