A study on the ultimate strength of ship plate with coupled corrosion and crack damage

Abstract

Under fatigue loading, crack damage shaped by stress concentration of pitting corrosion in the steel plate adversely affects the strength of ship structure. A nonlinear finite element study is carried out in this paper to investigate how coupled corrosion and crack damage influences the ultimate strength of ship plate. The parameters such as the length, angle and transverse position of cracks, corrosion density and depth and the plate slenderness ratio are taken into account in the present study. It is presumed that the crack is through-thickness and symmetrically distributed inside and on both sides of the corrosion pits, and no contact of crack faces occurs at the ultimate limit state. Reasonable crack gap and a shape of semicircular tip are employed based on numerical results. The crack propagation is not considered in this paper. It is found that the major crack impacts on the ultimate strength depend on the interactions between the length and location as well as the plate slenderness ratio. In addition, the effect of different corrosion factors can be attributed to the corrosion volume. When the crack and corrosion exist together in the plate, their reduction for the ultimate strength is less than their superposition when they exist alone. Moreover, the difference of these two reductions becomes larger as the crack angle increases. Based on numerical results, two mathematical formulas for predicting the residual ultimate strength of steel unstiffened plates with coupled corrosion and crack damage are proposed for longitudinal cracks, transverse and inclined cracks, respectively.