Large deformation elasto-plastic finite element analysis of plates, shells and tubular joints using semiloof shell elements

Irving, David (1982) Large deformation elasto-plastic finite element analysis of plates, shells and tubular joints using semiloof shell elements. (PhD thesis), Kingston Polytechnic,


In order to understand the collapse behaviour of thin shell structures, analysis procedures must simultaneously take account of both geometric and material nonlinearities. In the work presented the semiloof shell element has been developed within the LUSAS finite element system to account for geometric nonlinearities using a total Lagrangian formulation based on a large displacement, small rotation strain-displacement relationship, and material nonlinearities using a multilayer procedure based on the von-Mises yield criteria. A detailed description of the LUSAS finite element system and the newly developed facilities for, applying linear constraint equations, adopting transformed freedoms, increasing the flexibility. of the nonlinear procedures, and producing graphical output, is presented. The suitability of semiloof elements for large deformation analysis is assessed by examining the displacements and displacement derivatives obtained from tests on flat rectangular and quadrilateral elements under a series of 2nd, 3rd and 4th order out-af-plane displacement variations. A new technique has been incorporated in the nonlinear material procedure to optimise the number of sub-strain increments taken during plastic straining. Validation of the geometric nonlinearity has been ascertained by comparing results with a number of alternative analytical solutions, while results from the material nonlinearity have been compared to hand calculations based on fundamental plasticity theory. To obtain an insight into the behaviour. of the combin~d geometric and material nonlinear procedures adopted, a series of parametric studies have been carried out on plates and cylindrical panels subjected to inplane compression. A selection of these results, which quantify the effect of several important design tolerances, have been compared to a number of alternative analytical solutions. A study of currently recommended ultimate load design formulae for tubular joints has been carried out to determine each formula's predicted strength against experimental results. The review presented indicates the consistency of each formula for T,K and X joints over a wide parametric range. Both linear and nonlinear finite element analyses have been carried out on a series of tubular T-joint configurations tested experimentally under axial loading. The linear anaylses determine the magnitude and position of the stress concentrations, while results from the large deformation elasto-plastic nonlinear analyses show each joints full load deflection behaviour and ultimate strength compared to the experimental test. results. Finally the potential of the procedures adopted is shown by comparing the large deformation elasto-plastic load deformation behaviour of a large scale stiffened and unstiffened tubular T-joint to published experimental results.

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