| The use of aluminum alloy in shipbuilding and marine engineering is mainly based on welding structure.During the service period of the equipment,it is always subjected to continuous wave loads.Using the theory of fracture mechanics,the uninterrupted wave load can be regarded as welding.The structure is subjected to fatigue loads.Therefore,the mechanical properties and fatigue properties of the welded joints are very important for ships and marine structures.At present,scholars at home and abroad have extensively studied the fatigue properties of pure metal materials,but relatively few studies on the fatigue properties of welded structures.Therefore,strengthening the research on the fatigue properties of aluminum alloy welded structures is of far-reaching significance to the development of shipbuilding and ocean engineering.In this thesis,the marine high-strength aluminum alloy plate is selected as the base material,and the aluminum alloy flat plate butt welding process is studied and optimized.The microstructure and mechanical properties of the welded joints with good weld formation after non-destructive testing are studied;The fatigue crack growth rate test under different stress ratios of alloy base metal and welded joints,and the test results are analyzed,and the inherent law of fatigue crack growth behavior of marine aluminum alloy welded joints is obtained;The model was revised based on the residual stress to verify the accuracy of the revised model.In view of the above content,the main research work of this article is divided into the following aspects:(1)The use of aluminum alloys in ships and the status quo of fatigue crack growth of metal and metal welded joints are summarized.The research literature on fatigue crack growth behavior of metal materials and welded joints at home and abroad is integrated,and the research on fatigue crack growth rate prediction methods at home and abroad is analyzed and analyzed.In summary,determine the prediction model suitable for the fatigue crack growth rate of aluminum alloy materials in this thesis;(2)Carry out research on the microstructure and properties of welded joints of marine high-strength aluminum alloy MIG welding and pulse-assisted MIG welding,and analyze the effects of different welding process parameters on the microstructure,mechanical properties and fatigue of aluminum alloy welded joints The impact of performance,determine the optimal welding process plan for the flat plate butt welding of high-strength aluminum alloy medium and thick plates;(3)Carry out the experimental research on the basic mechanical properties and fatigue properties of the aluminum alloy base material and the welded joint before and after annealing,determine the relevant material parameters for the later test;conduct the fatigue crack growth rate test research on the aluminum alloy welded joint.The focus is on the fatigue crack growth rate of the aluminum alloy base material and the welded joint before and after the residual stress is eliminated under different stress ratios.The test results are summarized and analyzed and summarized.It is concluded that the different load ratios are for the aluminum alloy base material and the welded joint before and after the residual stress is eliminated.The influence of fatigue crack growth behavior;(4)The applicability of the existing forecast model is verified,and the forecast results and test results are compared and analyzed.The model was revised on the basis of the welding residual stress,and a fatigue crack growth rate prediction model suitable for welded joints was obtained.The test results and the prediction results were compared to verify the accuracy of the revised model. |
