Analysis On The Strength And Fatigue Strength Of Steel-Aluminium Joint At The End Of Superstructure

With the increasing emphasis on lightweight construction of ships,aluminium alloys have been widely used in the hull construction process.However,in order to ensure the overall structural strength in large ships,aluminium alloy materials are usually used only in superstructures.Due to the significant difference between the melting points of steel and aluminium,it is difficult to achieve direct welding of dissimilar materials.The use of steel-aluminium transition joints can effectively solve the connection problem.In order to study the steel-aluminium transition joint,this article analyses the structural strength and fatigue strength of the steel-aluminium transition joint when it is used in real ships.The main research contents include:(1)Based on the design wave principle,the COMPASS-WALCS-BASIC software is used to calculate the wave load of the target ship,and its maximum response value is selected.Then the whole ship model and the steel-aluminium transition joint model are established according to the drawings,and the calculated wave load is applied to the whole ship model through PCL language,and the response and deflection of the structure are solved.At the same time,observe the stress state of the steel-aluminium transition joint of two structural forms.For the area of stress concentration,fatigue analysis will be performed in the subsequent chapters.(2)First,the corresponding yield limit was measured through tensile tests of high strength steel and steel-aluminium transition joints of different structural forms,which served as a reference basis for the applied load in subsequent fatigue tests.Then the fatigue test was performed on the standard parts of the high strength steel of the cross joint and the steel-aluminium transition joint connection structure to determine the corresponding S-N curve.It provides a theoretical basis for the subsequent fatigue analysis of steel-aluminium transition joints in the real ship.(3)The principle of the spectral analysis method is described in detail,including the transfer function of stress response,the response spectrum of stress,the short-term distribution of stress range,the long-term distribution of stress range,and the calculation of fatigue cumulative damage.Combined with the characteristics of steel-aluminium transition joints,specific operational problems were explained,such as finite element modelling,the calculation of wave loads,the selection of hotspot locations,PCL automatic loading technology,the calculation of hotspot stress interpolation,and the extraction of stress,etc.,has formed the fatigue strength evaluation method of steel-aluminium transition joint based on the spectral analysis method.(4)Combined with the characteristics of the steel-aluminium transition joints,the fatigue strength analysis is carried out under full load conditions using full wave direction equal probability distribution wave load.For different fatigue hotspots,different S-N curves are selected to calculate the fatigue damage.At the same time,the D curve in the CCS fatigue specification is used as a reference group to verify the rationality of the selected S-N curve and detect whether the fatigue hotspots meet the requirements of fatigue design.