Analysis On The Fatigue Performance Of Steel-aluminium Joint Connection Structure

With the increasing demand for energy conservation and environmental protection in shipping industry,more and more attention has been paid to the lightweight of hull structure,and the use of aluminum alloy as superstructure material of large ships is one of the important means of lightweight.At the same time,in order to ensure the strength of the whole ship,the main hull is still made of steel material.In this case,it is necessary to solve the connection problem between the steel structure of the main hull and the aluminum alloy structure of the superstructure.At present,the technological method adopted is to connect them through the steel-aluminum composite transition joint.Because the composite joint is made by explosive welding,and the structural stress at the connecting part between the superstructure and the main hull is complicated,the joint often cracks due to fatigue factors,so it is necessary to study the fatigue performance of the joint structure.In this paper,the fatigue performance of typical hull steel-aluminum composite joint connection structure is studied by fatigue test method and structural fatigue evaluation method.The main contents include(1)Research on fatigue performance of marine steel aluminum composite joint:conduct tensile fatigue test of composite joint connection structure to obtain joint fatigue life curve;conduct shear strength test of composite joint structure to obtain joint shear strength;conduct shear fatigue test of composite joint to obtain joint shear fatigue life curve to guide subsequent design and calculation.(2)Simplified fatigue assessment method of composite joint connection structure based on empirical formula: Based on CCS "guide to ship fatigue strength 2018 edition",select typical sections,calculate the hot spot stress range of joint connection structure,and evaluate the fatigue life of selected joint connection structure according to the S-N curve obtained from the test.(3)Fatigue assessment of composite joint connection structure based on spectrum analysis: Based on spectrum analysis method,typical structure is selected at joint position,hot spot structure is refined by solid element,hot spot stress of selected joint is calculated directly by finite element method,and stress response spectrum of target ship is obtained by combining wave spectrum,and the whole fatigue damage accumulation process is regarded as piecewise continuous distribution,According to the statistical characteristics,the cumulative fatigue damage is calculated.In the calculation,the S-N curve obtained from the test fitting is used to evaluate the life of the nodes.(4)Research on fatigue performance research method: a fatigue performance research method based on shear stress as hot spot stress is established,which is compared with the previous research method based on principal stress as hot spot stress.It is used to determine the dangerous working conditions in the navigation process of the real ship,determine the dangerous stress conditions under the corresponding working conditions,and evaluate the life of the corresponding structure.