Research On Fatigue Strength Assessment Method For The Ship Typical Welded Joints

According to statistics,the catastrophic failure of the structure of ships,aircrafts and large-scale projects is mainly caused by fatigue.Complexity and randomness are two important features of the mechanism of metal fatigue.It is still worthy studying today to obtain the accurate fatigue mechanism of metallic materials and structures.Two commonly used methods in structural fatigue analysis are fracture mechanics and the S-N curve method.In the marine engineering field,S-N curve method is often used in fatigue analysis,of which key issues include external load calculation,stress calculation,distribution of the short and long term of stress and the selection of S-N curve.Orienting to the accurate calculation of the stress and the appropriate selection of the S-N curve,research on hotspot stress method,notch stress method and the selection of S-N curve are the main work in this paper.The hotspot stress method and notch stress method are used to analyze the fatigue of the typical welded joints of the ship.Main contents are as follows:1)Three kinds of hot spot stress calculation methods were interpreted in detail,namely traditional extrapolation method,Dong method and 1mm method.The models of different mesh size were applied to the four welded joints to calculate the results of the three methods.The advantages and disadvantages of the three methods and their scopes of application were analyzed.2)The notch stress of four welded joints were calculated based on simplified model or sub-model,and notch stress method were briefly analyzed by combining experimental data.A comparative analysis of the notch stress method was also made with the nominal stress method and the hotspot stress method.3)Two typical welded joints were selected as the fatigue test specimen.By using the least square method and maximum likelihood estimation to analyze experimental data,the S-N curve of the two welded joints was obtained.4)The external loads and stress of the ship structure are calculated,and hotspot stress method,notch stress method were used to analyze the fatigue strength of the welded joints.