The Research On The Ultimate Strength Assessment Method Of Ship Plates With Non-uniform Corrosion Wastage Based On The Fractal Theory

Marine structures such as ships are long exposed to sea environment,subjected to the erosion of sea water and atmosphere.When ships service for over 15-20 years,the effect of corrosion wastage on the ultimate strength of ship hull structures may become definitely serious.Further more,the extensive use of high strength steel makes the research of the ultimate capacity of hull structures more important.Many scholars at home and abroad have researched the grillage structures,but the irregularity of the distribution of localized corrosion was never taken into account effectively.This paper introduces the fractal theory for the simulation of corroded plate surface and focuses on investigating the influence of the irregularity of corrosion surfaces on the ultimate strength and developing a more accurate assessment method.The main work of the present study including:(1)introducing the fractal theory and constructing fractal brown surfaces by the mid-point displacement method for the fractal corrosion model of ship plates;(2)demonstrating the fractal and multi-fractal characteristics of both simulated surfaces and real surfaces gotten by scanning,then choosing and exploring the physical meaning of characteristic parameters;(3)simulating a series of fractal corrosion models and making corresponding FEA studies in ABAQUS;(4)investigating the relationship between the effective parameters and the ultimate strength,and making error analysis for the fitting formula;(5)expanding the value range of the aspect ratio and slenderness,then getting the formula with high adaptability;(6)making a comparison with other scholars’ methods and clarifying the effectiveness of the acquired formula.The simulated surfaces based on the fractal theory have a continuous trend and two controlling parameters which make any fluctuation possible.This method proves to be a much better practice in the simulation.For the formula derived,the coefficient of determination reaches 0.9628,which means the assessment method gotten has taken the irregularity of plate surfaces into consideration effectively.In general,this paper has maken the quantitative analysis of ultimate strength successfully and can provide a new reference for the inspection and repair of ships.