A Study On The Bending Stiffness Of Carbon Fiber Reinforced Plastic Box Girder

In the background of the current energy-saving and emission reduction,lightweight is one of the development trend of the bearing structure,especially in the vehicle body frame and aerospace application which is sensitive to the structural mass.The carbon fiber reinforced plastic(CFRP)box girder not only has the advantage of large inertia moment and torsion resistance because of the box section,but also high-strength and flexible design feasibility from the composite material.Therefore,the CFRP box girder has important application value as the bearing structure,it is necessary to study the bending stiffness and then to design the girder structure with excellent bearing performance.Most composite girder with the requirement of deformation is designed by choosing a laying scheme from experience currently,then the laying scheme and section parameters are optimized.This kind of design method is lack of systematic and need a lot of work.In this paper,the influence of the laying scheme and the section parameters on the bending stiffness of the CFRP box girder is analyzed systematically,which provides guidance for the design of the CFRP box girder.The research content includes the following aspects:Firstly,according to the elementary beam theory,the static analysis and deformation analysis of the box girder are carried out,according to the theory of folded plate,it is concluded that the overall bending stiffness of the box girder is equal to the sum of the bending stiffness of the flange and web.Based on the theory of composite single-layer lamina,the elastic constants of each layer are obtained.Then,the bending stiffness of the flange and web are obtained by the classical lamination theory.Then the bending stiffness calculation formula of composite box girder is obtained.Secondly,the influence of the laying scheme on the bending stiffness of the CFRP box girder is analyzed by FEA(finite element analysis)and experiment.The results show that increasing the proportion of 0 ° layer is helpful to improve the bending stiffness of the CFRP box girder.Finally,the influence of section parameters on the bending stiffness of CFRPbox girder is analyzed by FEA,including the height of girder section,the thickness of upper and lower flange,the thickness of upper flange.The results are as follows:(1)Increasing the height of the girder section,the thickness of upper and lower flange and the thickness of upper flange can effectively improve the bending stiffness of the CFRP box girder.And among them,increasing the thickness of upper and lower flange has the best effect on improving the bending stiffness of the CFRP box girder.(2)When the section parameters are changed,the changes of the bending stiffness of the CFRP box girder with different laying schemes are inconsistent.The higher the proportion of 0 ° layer,the smaller the change of bending stiffness.(3)In view of the improvement of bending stiffness of the CFRP box girder,the laying scheme can be analyzed first in the optimization,the methods are determined by the proportion of 0 ° layer.If the proportion of 0 ° layer is large,the section dimension and the thickness of the girder should be increased first.However,if the proportion of 0 ° layer is little,the height of the girder section,the thickness of upper and lower flange,the thickness of upper flange can be increased.