Research On The Influence Of Arbitrary Thickness Imperfections Or Circular Cutouts On Cylindrical Shell Axial Critical Buckling Load

Cylindrical shells with thickness imperfections and cutouts are widely applied in petroleum,chemical,aerospace and other industrial areas,and the forms of thickness imperfections and cutouts usually destroy the continuity of the shell structures and reduce their ability to resist axial buckling.In this paper,methods such as theoretical derivation,experiments and nonlinear numerical simulation are used to investigate the influence of these two factors on the shell axial critical buckling load.The main works are as follows.(1)A new theoretical method for the calculation of the critical buckling load of cylindrical shells with arbitrary thickness imperfections under axial compression is presented.Asymptotic formulas of buckling load,stress function and radial displacement are obtained.The relationships among buckling load reduction factor,non-dimensional thickness non-uniformity parameter and thickness attenuation wavelength parameter of shells with exponential thickness imperfection are also discussed.(2)The upgrading work on the axial buckling test platform such as increasing the size of worktable,reducing the distance between the pressure head and worktable,increasing the stroke of the pressure head,manufacturing concentric rings used to centering on worktable and realizing the synchronous acquisition of axial load and strain date are finished,and the measurement range of the platform and the accuracy and reliability of the measurement data are both improved.(3)A preliminary research on the influence brought by height and size of cutouts,thickness of penetrations are carried out with the method of finite element eigenvalue method,and an experimental scheme of shells with a circle cutout or a penetration subjected to axial load is formulated.A number of representative and relatively high precision cylindrical shells are manufactured,the tensile test of the material is carried out,and repetition measurements of shells' geometric parameters are finished.(4)Experimental study and nonlinear finite element analysis simulation of cylindrical shells with circle cutouts are carried out,a new modeling method based on the measured data of cylindrical shell with circle cutouts is put forward,the influence of ratio of cutouts,initial geometric imperfections,ratio of diameter to thickness and ratio of height to diameter and other factors on cylindrical shell with circle cutouts are investigated.(5)Experimental study of cylindrical shells with penetrations is carried out,the phenomenon and data in experiment are completely compared with the former experiment,namely experiment study of shells with circle cutouts.With the method of nonlinear finite element numerical simulation verified by the experimental results,the influence of initial geometric imperfections and penetration's thickness and other factors on axial critical buckling load of cylindrical shells with penetrations is studied,a definition of penetration thickness parameter is put forward,and its influence law on cylindrical shells with penetrations is also gained.