Cumulative Plastic Analysis Of Hull Members Under Cyclic Loading

Ultimate strength is one of the important contents of the safety assessment of hull structures.At present,the ultimate strength assessment of the hull structure is mainly based on the static limit strength of the structure,that is,the overall failure of the hull structure is considered to be caused by a one-time monotonous extreme external load.However,ships sailing in actual waves,under the action of multiple large alternating bending loads,the components farther away from the hull and the shaft will gradually produce cumulative plastic deformation,which will reduce the bearing capacity of the hull,and finally lead to the collapse and destruction of the entire hull beam.Aiming at this problem,this paper studies the calculation method of cumulative plasticity of hull components under cyclic load.The main research work is as follows:(1)Based on the Near-Field Peri Dynamic Differential Operator(PDDO),the calculation of cumulative plastic strain of hull components under cyclic load was carried out,and a numerical model of elastoplastic constitutivity based on PDDO was established.The numerical model of elastoplastic constitutive established in this paper is used to simulate the response of hull components under cyclic load,and the calculation results are compared with the finite element calculation results,which verifies the accuracy of the model in calculating the cumulative plastic strain of the structure.(2)Using nonlinear finite element method,the ultimate bearing capacity of stiffened plate under monotone load is studied.The influence of material model,initial defect and welding residual stress on ultimate strength of ship structure is considered.It will pave the way for the subsequent cyclic loading of stiffened plates.(3)using the isotropic hardening material model,has carried out based on PDDO elastoplastic constitutive model under cyclic loading method and nonlinear finite element method for the research on ultimate strength of stiffened plate,through the comparison of two methods to verify PDDO method in calculating the accuracy of the ultimate strength under cyclic loading,through comparative analysis with monotonic load calculation,The influence of accumulated plastic strain on ultimate strength of hull members was investigated.The ultimate strength and cumulative plastic strain response of the stiffened plate under constant amplitude and variable amplitude loading were studied.(4)with multiple ISSC2000 stiffened plate of plate frame structure as an example,carried out the monotonic loading and cyclic loading different role in the research on ultimate strength of the lower frame structure,under the action of cyclic loading is analyzed,the plastic strain of plate frame structure and the changing rule of the ultimate strength,explores the ultimate strength of hull structure under the cumulative plastic strain change rule.It lays a foundation for calculating the cumulative plasticity of ship hull under cyclic loading by using near-field dynamics method.