Equal Stiffness Analysis Method Of CFRP Tubular Structure

Carbon fiber-reinforced polymer?CFRP?is widely used in engineering due to its high specific strength,high specific modulus,light weight and high designability.As the cost of CFRP continues to decrease,it is gradually replacing metal materials for manufacturing.The character of CFRP plate structure is that the bending stiffness is relatively large but the torsional stiffness is weakness.and that makes it widely used to replace metal plate structure which requires large bending stiffness.However,it is difficult to replace the metal tubular structure which requires large torsional stiffness.This paper mainly studies the equal stiffness analysis method of CFRP pipe structure instead of metal pipe structure,and presents a set of efficient and accurate equal stiffness replacement and verification method.Firstly,the straight pipe is used as the basis model to analyze the influences from the layer angle and the layering sequence to the bending and torsion performance.Include:?1?0°shows the best bending resistance and 45°shows the best torsional resistance;?2?Considering the symmetrical layup,if only the laying angles,?and-?,are taken and alternately laid,the coupling effect between shearing and stretching does not exist,and the coupling effect between the twisting and bending is minimal;?3?Besides,the laying scheme[45°/-45°]_ns shows better bending and torsion resistance than other laying schemes which only take±45°;?4?Furthermore,the layering sequence[45°/-45°/45°/0°₂/-45°/45°/-45°/0°₂]_ns shows the same bending and torsional properties as steel.Secondly,according to influence of layering method on bending and torsion stiffness of pipe,an efficient and accurate equal stiffness design method for CFRP pipe is presented.The stiffness analysis method uses a straight pipe as a standard model.By analyzing the bending and torsion stiffness of the metal straight pipe and the CFRP straight pipe,a CFRP pipe with similar bending and torsion stiffness of the metal pipe section is obtained,and the layering scheme of CFRP is used as an equal stiffness layup corresponding to a metal pipe.Thirdly,the modal analysis is applied to the stiffness verification with the basis model of shaped pipe,and a full-modal stiffness verification analysis method is presented.The CFRP equal stiffness layering schemes for steel pipe with different thicknesses are verified by this verification method.Compared with the previous multi-case loading verification method,main advantages of the equal stiffness mode verification method are follows:?1?a simpler analysis process,this method only includes the modal analysis of replacement parts and original parts,which can greatly increase the verification efficiency;?2?the validity of this method is not limited by the loaded conditions of the structure,it can be applied in the equal stiffness verification of variable-loading structure;?3?The verification results,which are based on the theory of the stiffness matrix,are more reliable,and the all-round equal stiffness verification can be obtained.Finally,the CFRP stabilizer bar meeting the stiffness and strength requirements is obtained by using equal stiffness design and verification method,which proves the effectiveness of these methods.It is found that the CFRP stabilizer bar is 58.84%lighter than the steel stabilizer bar and has similar stiffness to the steel stabilizer bar,indicating that the equal stiffness analysis method proposed in this paper can be effectively applied to the equal stiffness design of CFRP tubular structure.The structure is lighter while retaining the same mechanical properties as the original structure.