Research On The Buckling Behaviors And Design Method Of Thin-walled Cylindrical Shell Structures Under Localized Axial Compression Loads

With the increasing function and safety requirements of large-scale engineering structures in modern industry,thin-walled cylindrical shell structures are constantly developing towards the direction of large-scale,light-weight and high-reliability.The increasingly stringent service conditions have made the external load conditions acted on them more complicated.Among them,a typical loading condition is the localized axial compression load,which is caused by the connection,restraint,action,or external environmental changes of adjacent structural components or auxiliary equipment for the thin-walled cylindrical shell structures.In this case,there is also a potential buckling risk for cylindrical shells.However,the current research on the buckling problems of thin-walled cylindrical shells under localized axial compression load is still very scarce,and there is few reliable buckling analysis and design method.Most of existing researches on the buckling problems of thin-walled cylindrical shells are based on the hypothesis of ideal uniform axial compression loading condition.It is also debatable that the established buckling design methods are applicable to the cylindrical shell under localized axial compression load.Based on this,the research on the buckling behaviors and design method of thin-walled cylindrical shell structures subjected to localized axial compression load are systematically carried out.The main research work and conclusions are summarized as follows(1)For the first time,the buckling experimental studies of thin-walled cylindrical shells subjected to localized axial compression load are performed.A database of initial geometric imperfections for metallic thin-walled cylindrical shells under one kind of specific manufacturing process is established.The strain curve,axial compression load-displacement curve,critical buckling load and buckling mode of the actual cylindrical shell under localized axial compression load are successfully obtained.The test results show that within a certain range,as the distribution scope of localized axial compression load increases,the critical buckling load of the cylindrical shell almost linearly increases;When the distribution scope of localized axial compression load exceeds 150°,its critical buckling load is close to the uniformly axial compressed cylindrical shell.(2)Based on the measured initial geometric imperfections,a numerical model for buckling analysis of locally axial compressed thin-walled cylindrical shell is established.After comparison,the error between the critical buckling load of simulation result and test result is 0.6%?11.7%,and the average error is about 6.3%.The feasibility and accuracy of the numerical model is verified.The deformation process and failure mode of thin-walled cylindrical shell under localized axial compression are clarified,and the buckling failure mechanism and the variation law of critical buckling load are also revealed.In addition,the effects of shell material property,structural characteristics as well as the relative position between the longitudinal welds and localized load on the buckling behavior of cylindrical shells are elaborated.(3)The sensitivity of thin-walled cylindrical shell structures under localized axial compression load to the measured initial geometric imperfections and local dent imperfections of is systematically studied.Specifically,the effects of the shape and amplitude of measured initial geometric imperfections on the buckling behaviors of cylindrical shell are analyzed,and the intrinsic reason why the measured initial geometric imperfections can affect the buckling load of cylindrical shell is also revealed;The effects of the amplitude,distribution scope,position and the different combination of local dent imperfections on the buckling load are investigated;What's more,the deterministic analysis numerical models that can effectively analyze the influence of oblique loading imperfection and uneven shell thickness imperfection are established,and the sensitivity of cylindrical shells to these non-traditional initial imperfections is discussed correspondingly.Finally,the reduction degree of the effect of non-traditional initial imperfections on critical buckling loads are quantitatively given.(4)A new method for predicting the elasto-plastic buckling load of thin-walled cylindrical shell structures under localized axial compression load is proposed,which can effectively consider the influence of initial imperfections.The limitation of the perturbation detection method in predicting the critical buckling load of axially compression loaded cylindrical shells is analyzed,and the fundamental reason is also discussed;According to the idea of the perturbation detection method,a new method for predicting the lower limit of elasto-plastic buckling load of a thinwalled cylindrical shell subjected to localized axial compression load is constructed,which is based on the extrapolation of the valley value in the detection reaction force-detection displacement curve.The feasibility and reliability of the new prediction method are verified by experimental results.(5)A design method for the lower limit of buckling of thin-walled cylindrical shells under localized axial compression load is established.With the consideration of the influence of elastoplasticity and the length-to-radius ratio,a modified calculation formula for the buckling load of cylindrical shell under uniform axial compression load is proposed.Then,a fast calculation formula for the buckling load of a locally axial compressed cylindrical shell is further established.The feasibility and accuracy of these formulas for actual application in engineering are validated;According to the proposed method for predicting the elasto-plastic buckling load of cylindrical shells under localized axial compression load,the concepts of plastic influence coefficient and structural characteristic parameter of a cylindrical shell are introduced,and a knock-down factor model based on buckling classification for the buckling load of axially compressed thin-walled cylindrical shells is constructed.Compared with the existing calculation models,the proposed model can simultaneously consider the effects of shell buckling failure type and the length-toradius ratio,which is safer and less conservative.