Research On The Ultimate Strength Of Hull Structures Based On Elastic Shakedown State Under Cyclic Loading

The ultimate strength of the hull structure is essential to guarantee the safety of hull structures.For a long time,the research on the ultimate strength of hull structures is based on the one-time static ultimate strength failure concept.Actually,the ship will be subjected to cyclic load caused by wave environment during the voyage.Conducting the study on the ultimate strength of hull structures under cyclic loading is beneficial to further understand the real mechanism of ultimate strength failure of hull structures.If the ultimate strength of the hull structure is placed under the cyclic load perspective,the hull structure may show elastic shakedown and plastic accumulation ultimate strength failure due to the different cyclic load patterns and amplitudes.Among them,the elastic shakedown ultimate strength failure is for the case where the amplitude is small and the plastic accumulation occurs only in the first few cycles.The plastic accumulation ultimate strength failure is for the situation where the amplitude is large and the plastic deformation accumulates after the hull structure exceeds the elastic shakedown state.In this study,the elastic shakedown state of the hull structure under cyclic loading is taken as the basis,employing the nonlinear finite element method,the ultimate strength and plastic accumulation characteristics of hull plates and stiffened plates in the elastic shakedown state and after exceeding the elastic shakedown state were studied.The main works are as follows:(1)The ultimate strength of hull plates under in-plane cyclic compression-tension loading in an elastic shakedown state is studied,and the effect of cyclic load amplitudes and other factors on the ultimate strength of hull plates under in-plane cyclic compression-tension loading in an elastic shakedown state is analyzed.In addition,the equations for the evaluation of the ultimate strength of hull plates under in-plane cyclic compression-tension load in the elastic shakedown state are given by the results of nonlinear finite element numerical calculations.(2)The nonlinear finite element analysis on the ultimate strength of hull stiffened plates under in-plane cyclic compression-tension loading in the elastic shakedown state is carried out.The effect of cyclic load amplitudes and other factors on the ultimate strength of hull stiffened plates under in-plane cyclic compression-tension load in the elastic shakedown state is investigated.(3)The series of nonlinear finite element analyses on the ultimate strength of hull stiffened plates under in-plane cyclic compression-tension loading in the elastic shakedown state were carried out.Based on the nonlinear finite element analysis,the average stress-average strain relationship of hull stiffened plates under in-plane cyclic compression-tension loading in the elastic shakedown state was obtained by modifying the average stress-average strain relationship of the Rahman beam-column method.(4)The study on the(residual)ultimate strength of hull stiffened plates after exceeding the elastic shakedown state under in-plane cyclic loading was carried out.The effects of cyclic load patterns and amplitudes,material properties on the plastic accumulation and(residual)ultimate strength of hull stiffened plates after exceeding the elastic shakedown state under in-plane cyclic loading were analyzed.(5)The study on the ultimate strength of a full-scale hull stiffened plate based on the elastic shakedown state under in-plane cyclic loading was carried out.The effect of welding residual stress changes and material properties on the ultimate strength of a full-scale hull stiffen plate in the elastic shakedown state under in-plane cyclic compression-tension loading was analyzed.In addition,the influence of plastic accumulation and(residual)ultimate strength of the full-scale stiffened plate after exceeding the elastic shakedown state under the cyclic load is discussed.