Study On Instability,axial Stiffness And Structural Optimization Design Of Aerospace Bellows

The bellows is a tubular component connected by foldable waves in the direction of folding and expanding,and it is widely used in aerospace,petrochemical,instrumentation,power,metallurgy,machinery and other fields.There are two main aspects of bellows for aerospace:one is using the waveform structure of the bellows to improve the stability of the structure,such as single C-shaped and C-shaped bellows,which are commonly used in large-diameter thin-walled pipelines;the other is using the axial tensile or compressive properties of the bellows,such as curved plate bellows,which are commonly used as elastic compensation components to absorb the displacement caused by mechanical or thermal loads in the pipeline.At present,there are few researches on the large-diameter bellows for aerospace,and the calculation error of the empirical formula used in the engineering is large.In this paper,the properties of single C-shaped bellows,C-shaped bellows and curved plate bellows in aerospace field are studied,mainly include the following:(1)The instability behavior of bellows under external pressure was studied by ANSYS APDL.The limit load analysis,eigenvalue and nonlinear buckling analysis were carried out for single C-shaped bellows,and the influence of various structural parameters on the instability property of the single C-shaped bellows under external pressure was clarified.It is concluded that the changes of critical instabiltiy load calculated by eigenvalue buckling analysis is basically the same as that calculated by nonlinear buckling analysis,and the value of the former is generally larger than that of the latter.The linear material model was used in the eigenvalue buckling analysis,and the calculated critical instability load may be greater than the plastic collapse load.The non-linear behavior of the material was considered in the nonlinear buckling analysis by ANSYS,and the critical instability load calculated is always less than the plastic collapse load calculated by the limit load analysis.The limit load analysis,eigenvalue and nonlinear buckling analysis were carried out for C-shaped bellows,and the influence of various structural parameters on the external pressure instability performance of C-shaped bellows was clarified.The buckling analysis of curved plate bellows was carried out,it is found that the type of their buckling was in-plane buckling,and more attention should be paid to their axial stiffness.(2)The axial stiffness of the curved plate bellows was studied by ANSYS APDL.The influence of structural parameters on the axial stiffness of the curved plate bellows was clarified.It was found that the thickness t,wave height h,radius R have great effect on the axial stiffness,and the other parameters have little effect on the axial stiffness.The axial stiffness increases with the increase of t and R,and decreases with the increase of h.Therefore,in the design,R can be taken as a fixed value according to the design conditions and the values of t and h can be changed to improve the axial compensive capacity of the curved plate bellows,and if the strength is not enough,the thickness of t can be appropriately increased.In addition,the axial stiffness of the curved plate bellows is smaller than that of the U-shaped bellows of the same size,that is,the curved plate bellows is easier to compensate the axial deformation.(3)In order to achieve the bellows structure with the best mechanical properties,the structure optimization design was carried out for single C-shaped and curved plate bellows for aerospace by the Response Surface Optimization of ANSYS Workbench.In the premise of a certain mass,the combination of structure parameters(wave radius r=43mm,wave pitch b=158mm,thickness t=3.1mm)of single C-shaped bellows were obtained when the critical instability load reaches the maximum value,and the combination of structure parameters(wave radius r3=33mm,wave pitch b=43mm,wave height h=58mm,thickness t=2mm)of curved plate bellows were obtained when the axial stiffness reaches the minimum.The structural performance of the carrier rocket directly determines the transportation weight,so it is of great significance to obtain the best structural performance through optimization design.(4)Based on the finite element calculations above,softwares were secondary developed for single C-shaped bellows and curved plate bellows by ANSYS APDL and VB.The calculation and check of single C-shaped bellows and curved plate bellows can be conducted only by importing the right structural parameters by using the developed softwares,even for the non professional analysis designer.