A Study On Static Mechanical Behavior Of CFRTP T-Joint Intended For Vehicle B-Pillar

With the increment of vehicle number,harmful gases emitted by cars have replaced dust as the main source of air pollution.In the face of climate change,many countries,including China,have been introducing increasingly stringent emission regulations.One of the most effective methods to reduce the fuel consumption and emission of automobiles is to make them lighter.There are tests show that every 10%reduction in vehicle weight leads to a fuel consumption reduction by 6%～8%and an emission reduction by 4%.At the same time,the lightweight can directly improve vehicle specific power and dynamic performance.Using CFRP instead of traditional metal materials is the most effective way to achieve it.CFRTP(Carbon Fiber Reinforced Thermoplastic),compared with thermoset CFRP,have same advantages of specific strength,specific stiffness,designability,corrosion resistance,etc.,furthermore,have better characteristics of low density,no need for refrigeration,fast molding,renewability,etc.,and therefor are more suitable for mass production of modern industrial.While considering the vehicle lightweight,we also need to pay attention to the safety.When the side enclosure occurs,B-pillar and its lower T-joint play an important role.The upper branch of the T-joint is connected to the B-pillar of the automobile,while the left and right branches are connected to two threshold beams,which makes the structure complex.As an important part of vehicle frame,the bottom T-joint of B-pillar has a significant influence on the stiffness and strength of the vehicle.At present,a few scholars have studied the thermoset CFRP T-joint,but there has been no research on CFRTP.The research on CFRTP is mainly concentrated in Japan,the United States and other developed countries.Therefore,this paper chooses to study the CFRTP T-joint,which has a certain guiding significance for the application of CFRTP in vehicle lightweight and the comparison between CFRTP and thermoset CFRP.The CFRTP T-joint is designed according to characteristics of CFRTP and parameters of a traditional T-joint.Depending on the equipment and the prepreg we have,compression moulding forming is used to make CFRTP laminates,and corresponding moulds are made for it Next,the mechanical properties of CFRTP laminates are tested following ASTM standards.In order to evaluate the performance of CFRTP T-joint,a quasi-static transverse bending test,and another with torsion,are conducted.The results show that,for the T-joint structure,the hat shaped laminate is more important than the flat laminate,and the main factor limiting the joint’s transverse bending performance is the shear strength of the two wings of the hat shaped laminate,while the torsion strength is limited by the connection strength of the two sides of the central branch.After damages of CFRTP joint are analyzed,accurate FEM simulations are carried out with Abaqus.And the results are basically consistent with the tests.The specific strengths of CFRTP and thermoset CFRP are compared.Moreover,performances of joints made of them are compared using FEM simulation.The results show that CFRTP is not as good as thermoset CFRP in strength,but has an advantage in stiffness.Finally,the optimal design of CFRTP layer number and angle is carried out aiming at maximum stiffness and minimum mass of the joint,which makes the joint stiffness greatly improved while the mass is reduced.The result indicates that directions of laminates have a significant influence on the performance of a composite joint.That is because the directions of fibers can change the stress situation at the critical position greatly.