Experimental And Simulation Analysis Of Fatigue And Load Capacity Performance Of Aluminum Alloy Grillage

With the development of ship towards to large-scale,the demand of lightweight structures of ship is increasing.Aluminum alloy is widely used in ship structures due to its low density(about one-third of steel),high strength and anti-corrosion characteristics.However,few studies are conducted on the fatigue performance of aluminum alloy ship structures and it is difficult to evaluate the fatigue strength of aluminum alloy structures for great difference in performances of mechanical characteristics of aluminum alloy before and after welding.Currently,the research work on the aluminum alloy structure mainly concentrates on the experiment and numerical simulation of small size specimen,such as standard tensile specimens and the welded joints.Few experimental investigations are carried out on the fatigue strength of welded aluminum alloy structures with real scale.In this paper,the fatigue strength and load capacity are conducted on the real-scaled welded aluminum alloy grillage structure.The curve of fatigue-life with loads of welded aluminum alloy grillage structure is derived.The effect mechanism of welding defects and welding type on the load-capacity is revealed.Firstly,the ultimate load-capacity of aluminum alloy grillage structure is obtained by the experimental studying.The numerical simulation is investigated on the ultimate load-capacity of aluminum alloy grillage structure based on true stress-strain curve of the material and the failure strain corresponding to the element size.The numerical simulation results are compared well with experiments.Then,non-destructive testing is performed on the welds of the aluminum alloy welding grillage structure.The weld defects are divided into two categories according to the flaw detection results.The fatigues loads are divided into three levels depend on the ultimate load-capacity experiment results.Besides,two kinds of aluminum alloy grillage fatigue experiment are carried out.The fatigue life and failure modes of two types of aluminum alloy grillage structure are obtained.The effect law of welding defects on the fatigue life and failure mode of aluminum alloy grillage structure is clarified.The curve of fatigue-life with load of aluminum alloy grillage structure under repeated loads is gained.Finally,the numerical model with different welding defects of local structures is built.The static analysis is conducted on the numerical model.The law of stress field distribution is obtained.The mechanism of fatigue crack initiation is revealed.The numerical simulation is conducted on the effect of welding type on the ultimate load-capacity.The mechanism of welding type on ultimate load-capacity of the aluminum alloy grillage structure is revealed.