The Research On Ultimate Strength Of Ship Plates With Non-uniform Pitting Corrosion Wastage

It is hard to avoid the ultimate strength declining due to corrosion damage for ships and offshore structures in the marine environment. And the buckling failure phenomenon of ship hull girders is more frequently happened with extensive use of the high-strength steels, while the corrosion damage making it even worse. So it is meaningful to estimate the buckling ultimate strength accurately.The influence of corrosion location distribution on ultimate strength was generally ignored by researchers at home and abroad. However, the non-uniform corrosion is common in hull structure, and it was often resulted in the unexpected accident due to features of chanciness and suddenness.Therefore, the aim of the present thesis is to investigate the ultimate strength characteristics of high-strength steel plates with different corrosion location types. A series of ANSYS non-linear finite element analysis are undertaken.The main work of the present thesis includes:(1) Establishing finite element model of non-uniform pitting plates and trying to narrow the gap with actual structure then reducing the model uncertainty mostly; (2) Calculating the ultimate strength reduction factors due to different localized corrosion under axial and biaxial compressive loads; Making sure the dangerous area of the plate; (3) Having a sensitivity analysis to confirm the effect of the aspect ratio a α plate slenderness ratio β loading ratio cp and other corrosion parameters; (4) Ensuring the modal distribution of block type local corrosion, then forming a grader rules; (5) Providing a ultimate strength assessment method by numerical fitting.It is proved that different types of corrosion location can lead to distinguishing results. The single-side type pitting corrosion located in the short edge is the most dangerous under axial compressive loads; while the area changes from boundary to center with the increase of load ratio under biaxial compressive loads. It is also proved that the proposed ultimate strength assessment approach is easy and useful for engineering evaluation. The design formulae and grader rules obtained from the present study can give an important reference for ultimate strength assessment of non-uniform pitting plates.