Research On Ultimate Strength Of Stiffened Plate Based On Polar Ship-ice Collision

With the rapid development of polar resources and routes,polar ship-ice collision accidents are gaining more and more attention.And the design method based on ultimate limit state is introduced as one of the most important means to measure the safety of hull structure,which can take into account the material properties and the permissible plastic deformation of the structure.Therefore,it is of great significance to study the ultimate strength of the stiffened plate based on the polar ship-ice collision.The research results can improve the safety and economic benefits of the hull structure in the design of the polar ship.The ultimate strength of stiffened plates considering the effects of material properties and dent damage was comprehensively studied based on polar ship-ice collision.In order to simulate the dynamic process of ship-ice collision accurately:(1)the constitutive relation of EH36 steel for polar ship steel was studied by experimental method,(2)combined with the isotropic three-dimensional failure criterion,a multi surface failure sea ice constitutive model based on linear elasticity was proposed.On this basis,the ultimate strength calculation method of stiffened plate considering material characteristics was proposed.And the change trend of ultimate strength of stiffened plate under different temperature and loading rate was analyzed.At last,the influence of low temperature,strain rate and impact dent on the ultimate strength of the stiffened plate were discussed in combination with the calculation of the residual ultimate strength of the stiffened plate with impact dent damage under several typical ship-ice collision conditions.The specific research contents are as follows:(1)A dynamic constitutive model of EH36 steel considering low temperature effect was proposed.According to the quasi-static tensile test results of EH36 steel at five typical temperatures,the relationship between temperature reduction and yield strength of EH36 steel was fitted.According to the tensile test of EH36 steel at low strain rate,and the impact compression test of EH36 steel under high strain rate and ultra-high strain rate,it was found that EH36 steel is strain rate sensitive material.Based on the Cowper-Symonds model,its viscous parameters and strain rate hardening parameters were fitted.On this basis,a dynamic constitutive model of EH36 steel considering low temperature effect was proposed.(2)A sea ice constitutive model suitable for ship-ice collision research was proposed.Based on Derradji-Aouat isotropic three-dimensional failure criterion and elastic brittle failure mode,multi surface failure sea ice constitutive model based on linear elasticity was proposed.And corresponding solver was compiled by using secondary development application in LS-DYNA.After verifying the accuracy of the solver,the dynamic response of cylindrical ice impact on the side plate of ship was analyzed.(3)A method for calculating ultimate strength of stiffened plates considering material properties was proposed,and the influence of low temperature and strain rate on ultimate strength of stiffened panels was studied.On the basis of the study of the dynamic constitutive model of EH36 steel,the calculation of the ultimate strength of the stiffened plate during the dynamic axial compression was realized by using LS-DYNA.The ultimate strength of stiffened plates under the influence of several typical temperature and strain rates was calculated by the finite element method.According to the calculation results,the influence of the low temperature and strain rate on the ultimate strength was fitted.(4)The influence of collision dent damage on ultimate strength of stiffened plates was studied.According to the finite element calculation results of the residual ultimate strength of stiffened plates under multi group ship-ice collision conditions,the influence of impact dent damage on the ultimate strength of stiffened plates was fitted.In connection with the effect of characteristics of steel,a computation model for ultimate strength of stiffened plates considering low temperature,strain rate effect and impact damage was proposed.