Experimental Research And Numerical Analysis Of Axial Elastic And Plastic Buckling Of Welded Cylindricalshells

Welded cylindrical shells have a wide application in petroleum, chemical, metallurgy, environmental protection and other industrial areas. The common characteristics of such structures are small wall thickness and large ratio of radius to thickness, which make them vulerable to axial buckling failure. In this paper, experimental and numerical methods are adopted to investigate on axial elastic and plastic buckling of welded steel cylindrical shells. The main works are as follows.(1) A circumferential geometric imperfection disturb method is proposed to calculate the axial elastic branch buckling load of cylindrical shells. Using the proposed method, the controversial issue "whether weding residual stress is favorable or unfavorable to axial elastic buckling critical load" is explored; the effect of the existence and size of local geometric depression on axial elastic buckling is analyzied.(2) An axial buckling test platform with automatic acquiring function of initial geometric imperfections and axial loading function is developed independently. The test platform adopts a frame structure form and assembles geometric imperfections measuring system, axial loading system and control system into one whole. The geometric imperfection measuring and axial loading of specimen can be finished by positioning the specimen only once during the test. The advantages of this test platform are high scaning accuracy of geometric imperfections, large nominal axial load and friendly human-computer interaction. It is suitable for experimental research of axial plastic buckling of cylindrical shells.(3) Several typical cylindrical shell specimens are made. Experimental study on axial plastic buckling of combined cylindrical shells with reinforcement is carried out by using the independently developed buckling test platform. The effect of weld type, the number of circumferential welds, the amplitude of weld reinforcement, the material yield strength and the polish of weld reinforcement, etc. on the axial plastic buckling is explored.(4) A finite element analysis model, which considers initial geometric imperfections and welding residual stress, for learning axial plastic buckling of cylindrical shells with weld reinforcement is established and its corectness is verified by using existed experimental results. The effect of the existence and maginitude of welding residual stress on axial plastic buckling is analyzed. The mechanism of why welding residual stress has an effect on axial plastic buckling is revealed from the point of stress variation of the inner and outer surface of buckling zone. (5) A numerical method used for predicting the axial plastic buckling critical load of welded cylindrical shells with reinforcement is proposed and its corectness is verified by using existed experimental results.