Research On The Ultimate Load Bearing Capacity And Failure Mode Of Stiffened Plates With Pitting Corrosion

Corrosion is inevitable in ships because of the harsh marine environment.As the basic unit of steel plated structure,the corrosion of stiffened plates can reduce the strength of the hull,which may lead to cracks,brittle fracture,instability and other damage of ships.The corrosion of ships can be divided into general corrosion and localized corrosion.Pitting corrosion is a typical corrosion form in localized corrosion.The complexity of pitting corrosion makes it difficult to calculate the ultimate strength of the structure.Due to the local characteristics and the stress concentration caused by pitting corrosion,the effects of pitting corrosion on the mechanical properties of structures are even more heavier than that of general corrosion.In order to investigate the influence of pitting corrosion on the ultimate load bearing capacity and failure mode of stiffened plates,the following work has been done in this paper.The effects of the parameters of pitting corrosion(pit diameter,pit depth,pitting induced eccentricity)and the parameters of corrosion degree(corrosion volume loss,cross section area loss,DOP(degree of pitting))on the ultimate load bearing capacity and failure mode of the stiffened plate were studied by axial compression test of 10 stiffened plates.It can be seen that the pitting corrosion can cause significant changes in the redistribution of internal forces of each component(flange,web,plate)of the stiffened plate.The ultimate load bearing capacity of the stiffened plate decreases with the increase of the pitting diameter and depth of web or plate.When the web is seriously corroded in only one side,the stiffened plate is prone to fail by stiffener tripping because of the additional bending moment caused by eccentric pitting corrosion.The uniaxial load bearing capacity of corroded stiffened plates is strongly related to the section area loss,and the failure mode of the stiffened plate is closely related to the relative section area loss.The commercial finite element analysis software ABAQUS was used to analyze the buckling of the stiffened plate.The accuracy of numerical simulation was verified by the simulation of the test specimens.Based on the tests,some special corroded specimens were simulated to investigate the failure mechanism of stiffened plates,and the conceptual models of plate buckling and stiffener tripping failure were presented.In addition,more corrosion range samples were simulated to investigate the influence of corrosion degree parameters on the ultimate load bearing capacity and failure mode of the stiffened plate.The result showsthat the section area loss is closely related to the residual strength of the corroded stiffened plate.The stiffened plates of different sizes in the engineering application range were simulated to investigate the effects of the stiffener slenderness on the failure mode of the stiffened plate.Based on four intact stiffened plates,the effects of pitting corrosion on the failure mode of the stiffened plates with different slenderness was discussed.With the increase of the stiffener slenderness,the failure mode of stiffened plate changes from stiffener tripping to overall buckling.The failure mode of the stiffened plate mainly depends on its original size,and only one failure mode was observed for each stiffened plate after pitting corrosion except the base failure mode of the intact stiffened plate.When the stiffened plate has a large stiffener slenderness,the tripping failure mode no longer appears even if the relative section area increases.In addition,the empirical formulas for the strength calculation of stiffened plates were compared with the experimental and simulated results,and the applicability of the design formulas is analyzed.The result shows that after the effective section area is corrected by the corrosion section area loss,the ultimate strength of the pitted stiffened plate could be accurately predicted by Faulkner’s formula.