Research On Buckling Behavior Of The High-Altitude Test Chamber And Thin-Walled Cylindrical Shells With Large Rectangular Openings Under External Pressure

With the development of China’s aerospace industry,the demand for experiments in the space environment has increased rapidly.The high-altitude test chambers used to simulate the working environment of aircraft engines sometimes need to have large rectangular openings due to testing and process requirements.The existence of large rectangular openings would cause disruption of the geometric continuity of the structure,leading to a decrease in its critical buckling load and ultimate bearing capacity.Based on the finite element analysis method,the strength and buckling analysis of a high-altitude test chamber were conducted firstly in this thesis.Secondly,taking the thin-walled cylindrical shell structure with a large rectangular opening derived from the test chamber as the research object,the influences of different factors on its critical buckling load and buckling behavior were studied.The main research contents and conclusions are summarized as follows:(1)Based on the theory of linear elastic analysis,a finite element analysis model of the high-altitude test chamber was established using the finite element analysis software ANSYS Workbench according to the design and process requirements.The static structural analysis of the high-altitude test chamber was carried out under the design conditions.The results of its stress distribution and deformation were obtained,and the strength and fatigue verifications were carried out.The results indicated that the high-altitude test chamber met the design requirements and would not experience the strength and fatigue failures.(2)Based on the theories of structural buckling,the buckling analysis was conducted for the high-altitude test chamber,obtaining the 1st to 6th buckling modes and load factors of eigenvalue buckling,as well as the entire buckling process under nonlinear conditions.The results indicated that the instability of the high-altitude test chamber under eigenvalue buckling occurred in the top area of the long section of the cylinder,with a linear critical buckling load of 1.656 MPa.The instability of the high-altitude test chamber under nonlinear buckling occurred at the connection between the short section of the cylinder and the head,and its nonlinear critical buckling load was 0.858 MPa,which met the design requirements.The deformation at the midpoint of the large rectangular opening length was relatively large,but the von-Mises stress value was relatively small,and always less than the yield strength of the material.The deformation at the upper right corner of the large rectangular opening was relatively small,but its von-Mises stress value was relatively high,which could first reach the yield strength limit of the material in the nonlinear analysis.(3)The thin-walled cylindrical shell structure with a large rectangular opening was taken as the research object,and its eigenvalue buckling and nonlinear buckling behavior were analyzed.The influences of different geometric factors and material parameters on the critical buckling load and buckling behavior of the structure were studied.The results indicated that the main influencing factor of its critical buckling load was the ratio of the structure’s diameter to thickness(R/t).As the yield strength increased,the critical buckling load and maximum displacement of the structure also increased.The maximum deformation was located at the midpoint of the rectangular opening length boundary,and the von-Mises stress showed a linear increase first,followed by a decrease and then a rapid increase.(4)For the thin-walled cylindrical shell structure with a large rectangular opening,structural reinforcement was carried out by stiffeners,and the influences of different positions and sizes of stiffeners on the critical buckling load and buckling behavior of the structure were investigated.The results indicated that when the size parameters of stiffeners were 150×150×8×12 mm and the position parameters were 27°×1300 mm,the critical buckling load of the structure was the highest,reaching 1.231 MPa,which was 40.85% higher than that of the unreinforced structure.The maximum deformation was located at the midpoint of the large rectangular opening length boundary,which was107.71 mm,and was 50.38% lower than that of the unreinforced structure.In the nonlinear buckling analysis,the von-Mises stress of the stiffeners increased with the increase of the load,while the von-Mises stress of the cylindrical shell structure showed a trend of first increasing,then decreasing,and then increasing with the increase of the load.The stiffeners could first undergo yield failure,causing them to lose their reinforcement effect on the thin-walled cylindrical shell structure.