Equivalent Wall Thickness Criterion And Analysis Of Springback Prediction For Bimetallic Composite Tube Bending

Bimetallic composite pipe is a kind of metal tube,which is made of two metallic materials through the mechanical combination.Such as copper-titanium bimetallic composite tube,with the good electrical and thermal conductivity of copper materials and the high strength,high rigidity and good corrosion resistance of titanium materials,it commonly used in aerospace and other fields.The springback of bimetallic composite tube’s bending process is its unique nature,and the bending process involves the coupling between two different metals,so the theoretical analysis is more difficult.This paper proposes an equivalent theory for the composite tube springback,theoretical prediction of the bending springback of the composite tube through the equivalent criterion to solve the problem.The main research contents of this paper are as follows:Firstly,the deformation law of common single-layer tube bending and the difference between composite tube are analyzed.The intrinsic model of tube is reasonably selected,the stress-strain of tube bending is introduced based on the basic assumptions,and the bending moment formula of single-layer tube considering the change of ellipticity of tube cross-section is calculated.The bending moment formula of composite tube bending is further introduced,and the theoretical reliability is verified using finite element simulation.Secondly,based on the unloading law and bending moment equation,the analytical equation of tube bending springback theory is derived and a numerical simulation model of tube bending springback is established to verify the springback theory.The numerical simulation model of composite tube bending springback was established,and the limitations of the springback formula were found.The influence of the coupling effect of composite tube base and cover tube on the springback angle was analyzed,and it was found that the composite tube springback was the result of the joint action of base and cover tube;the equivalent equivalence criterion and equivalent wall thickness criterion theory were proposed,and the equivalent springback formula of composite tube was introduced through the equivalent theory,and the preliminary verification was carried out through numerical simulation.Finally,the equivalent springback theory is further studied to analyze the causes of errors,and the scope of application of this theory is obtained through a combination of theoretical analysis and simulation to verify the accuracy of theoretical prediction.The effects of fluctuations in wall thickness ratio,bending angle,cross-sectional ellipticity,relative bending radius,the outside diameter of tube,the wall thickness of tube and material strengthening curve parameters on the springback were studied,and this composite tube equivalent theory was improved to some extent.The forming prediction and springback angle compensation system is established,which can easily calculate the data under different parameters.